I spent the summer of 1970 working full-time in Prof. Ethan Signer’s laboratory at the Massachusetts Institute of Technology while taking one last humanities course needed to complete the requirements for my undergraduate degrees from MIT in Life Sciences (course 7) and Electrical Engineering (course 6). Ira Hershkowitz, an advanced graduate student in Signer’s lab at the time, served as my direct supervisor, providing me with a crash course in bacteriophage lambda and its host, E. coli, to enable me to successfully perform the project assigned to me by Prof. Signer. This project involved the development and use of a method to isolate successfully non-leaky amber mutants in the red (i.e., recombination) genes of phage lambda. This work was eventually published as J.E. Mertz, E.R. Signer, & F. Schaefer, Amber red- mutants of phage lambda, Virology 1975 Feb;63(2):591-5. doi: 10.1016/0042-6822(75)90332-3.
In August 1970, I attended my first scientific conference, Bacteriophage Lambda Workshop, held at the Cold Spring Harbor Laboratory. Attendance at this conference, in combination with the research I had performed that summer, provided me with much knowledge that was relevant soon thereafter to my developing (in collaboration with postdoc Douglas Berg) the first potential cloning vector (i.e., lambdadvgal120) and my discovery (in collaboration with Assistant Professor Ronald Davis) that the EcoRI restriction enzyme leaves ligatable cohesive ends when it cleaves DNA, similar to the cohesive ends present in phage lambda DNA when it is packaged into virion particles.
Other Materials in Boxes 1-4
I arrived at Stanford University in September 1970, ready to begin graduate school there in the Biochemistry Department located in the Medical School. I was one of six students admitted to this graduate program that year. Other members of my class included Randy Schekman (2013 Nobel Prize in Physiology or Medicine), Paul Hagerman, Steve Reed, and Paul Schedl. I was the third female student admitted to the department since its founding in 1959 and the first female student admitted in 9 years.
The six of us spent the fall quarter at Stanford taking a few classes (including the Medical School’s Biochemistry course taught by our faculty) and talking with the professors in the department and members of their labs with whom we thought we might desire to do our Ph.D. thesis research. I seriously considered Profs. A. Dale Kaiser, David Hogness, and Paul Berg. Berg told me about the research he was proposing to perform in a grant application he was submitting in November 1970 to the American Cancer Society. A postdoctoral fellow in his laboratory, David A. Jackson, had already begun work on this project in 1969 (either before or as soon as Berg arrived back at Stanford after his 1968-1969 sabbatical year in Renato Dulbecco’s lab at the Salk Institute where Berg and his lab manager, Marianne Dieckmann had learned about how to work with polyoma viruses). In this grant application, Berg wrote about creating a trivalent recombinant DNA molecule in a test tube. This recombinant would consist of the genome of the DNA tumor virus SV40 joined covalently to a deleted variant of phage λ (i.e., λdv) containing both the λ genes needed for replication as an autonomous plasmid in its E. coli host and the genes from E. coli needed for utilization of the sugar galactose (i.e., gal operon). Berg proposed to anneal together SV40 and λdvgal by addition of complementary tails to the ends of the two DNAs using the enzyme terminal transferase and to covalently join them together using E. coli DNA ligase after filling in any gaps with DNA polymerase. Once these recombinant DNAs had been successfully generated, the plan was to put them into both mammalian cells and E. coli to look for DNA replication and possible expression of the foreign genes. In mammalian cells, the plasmid DNA would replicate via the SV40 replication machinery and sometimes integrate into the mammalian host DNA at frequencies dependent upon the host species. In E. coli, the plasmid DNA would replicate via the phage λ genes. One could then ask a variety of questions including the following:
1. Would the gal operon from E. coli be expressed in mammalian cells?
2. Would SV40 DNA replicate in E. coli and, if so, could this method be used to replicate non-viable mutants of SV40 for subsequent study back in mammalian cells?
3. Might any of the SV40 genes be expressed in E. coli?
Dave Jackson was already working in fall 1969 (in parallel with Peter Lobban, a graduate student in Kaiser’s lab) to develop this terminal transferase method for joining DNAs in vitro. If successful, Dave planned to answer question 1. Berg suggested that I could work on answering questions 2 and 3 for my thesis project once Dave had succeeded in making the SV40-λdvgal recombinants.
In December 1970, I officially joined Berg’s research group. Given the recombinant SV40-λdvgal DNA was not yet in hand, Berg proposed I work on three other projects in the interim:
I. Isolate a λdvgal containing the entire gal operon and find a method for successfully reintroducing this plasmid back into E. coli from purified DNA.
II. Determine whether the SV40 DNA genome can be at least partially expressed when transfected into monkey cells in a form other than its native superhelical, double-stranded circular DNA, i.e., nicked circular, linear, denatured, or single-strand circular DNA.
III. Study the formation, structures, and properties of defective SV40 genomes that arise naturally when the virus is passaged in monkey cells at high multiplicities of infection.
I immediately began work concurrently on all three projects, starting first by learning the methods needed to perform the experiments. Given I was working on several projects concurrently, I split my laboratory notebooks into Chapters, with each numbered Chapter devoted to a project or method. These looseleaf pages were originally contained within sequential, Roman numeral-labeled 3-ring binders, with each binder having a Table of Contents page at the front. Experiments performed during overlapping time periods were typically included within the same binder, with the experiments on a given project ordered chronologically within its own Chapter (rather than intermixing project pages to maintain strict chronological order). When a project continued over numerous months, e.g., when variations on the experiments were repeated multiple times, its Chapter was often continued over two or more 3-ring binders, with each repeat labeled by a new digit after the decimal point placed after the Chapter number.
I. Isolation of the bacterial cloning vector λdvgal120 and its reintroduction into E. coli.
Kaiser’s lab had developed a method for successfully introducing purified linear whole phage λ DNA into E. coli (Mandel & Higa, J Mol Biol. 53:159-62, 1970). Chapter 9 (box 1, folder 2) contains the first of the series of experiments I performed toward showing that this method also worked for circular plasmid DNAs such as λdvgal120. In Chapter 9, I was using phage λ DNA to learn the method with help from Peter Lobban. These experiments continued with plasmid DNAs in Chapter 21 (box 1, folder 5) which contains my experiments from spring 1971 using the calcium method of Mandel & Higa to introduce highly purified λdvgal120 plasmid DNA into E. coli where it was replicated and expressed. Page 21.4b shows my succeeding in May 1971 in transforming E. coli with λdvgal120 at an efficiency of ~ 1 gal+ colony per 10E6 DNA molecules. This experiment proved that this method worked for plasmid DNAs as well as linear phage DNAs. Paul Berg informed Stanley Cohen (a then-Assistant Professor of Genetics whose laboratory was located just down the hallway from ours) of this finding given this method would be extremely useful for Stan’s studies with R-factor plasmid DNAs and had me give Stan a copy of my protocol. Stan then proceeded to learn how to get this protocol to successfully work with help from Peter Lobban (after L. Hsu, an undergraduate student in Cohen’s lab, had been unsuccessful trying to do it since fall, 1969?). The Cohen lab article was published as S. N. Cohen, A.C. Chang, & L. Hsu, Proc Natl Acad Sci USA. 69:2110-4, 1972. We didn’t bother to publish our prior finding about transformation of plasmid DNA into E. coli until 1974 (see below) because it was not central to our research.
Chapter 19 of box 1, folder 2 (and beginning of box 1, folder 3) contains the experiments I performed (in collaboration with Douglas Berg, a postdoctoral fellow in Kaiser’s lab) to isolate and characterize λdvgal120, a plasmid that is a deleted variant of a phage λ (obtained from Mike Feiss, a postdoctoral Fellow at the time in Allen Campbell’s laboratory in the Biology Department at Stanford) that contained the entire gal operon of E. coli. λdvgal120 lacks most of the genes from phage λ other than ones needed for its replication as an autonomously replicating plasmid. This is the plasmid DNA used later by both Jackson and me to create our SV40-λdvgal recombinant DNAs by the terminal transferase and EcoRI/ligase methods, respectively. A paper describing our work with λdvgal120 (including how to transform it back into E. coli) was published as D. Berg, D.A. Jackson, & J.E. Mertz (Isolation of a lambda dv plasmid carrying the bacterial gal operon. J Virol. 14:1063-9, 1974). David Jackson contributed to the purification of this plasmid DNA and its physical characterization while Doug and I performed its isolation and genetic characterization.
II. Studies on infectivity of different forms of SV40 DNA, leading to discovery of easy, highly efficient method for creating recombinant DNAs in vitro using EcoRI restriction endonuclease followed by E. coli DNA ligase.
Chapter 17 (box 1, folder 2), Chapter 20 (box 1, folder 3), Chapter 22 (box 1, folder 5), and Chapter 31 (box 1, folder 6) contains the series of experiments I performed to look at the infectivity of different forms of SV40 DNA., i.e., nicked circles, denatured, single-stranded circles, and linearized SV40 DNAs, compared to native superhelical, double-stranded circular SV40 DNA, i.e., SV40(I). These data provided an early indication that linearized SV40 DNA has 8% - 10% the infectivity in monkey cells as does native SV40(I). In April 1971, I examined the infectivity of the DNA Jackson had linearized by incubation of SV40 circular DNA with DNase I in the presence of manganese. When it exhibited about 1/10th the infectivity of native superhelical DNA (page 17.2c), we assumed it was due to DNase I sometimes leaving staggered nicks in the DNA rather than straight across blunt ends when it cleaved the two strands. However, when John Morrow (another graduate student in Berg’s lab one year ahead of me) discovered in the summer of 1971 that EcoRI restriction endonuclease cleaves SV40 DNA once at a unique site (J.F. Morrow & P. Berg, PNAS 69:3365-9, 1974), I repeated the experiment to determine the infectivity of linearized SV40 DNA, this time using DNA linearized by cleavage with EcoRI, i.e., SV40 (LRI).
Chapter 22 includes my key, somewhat surprising finding that linears generated by cleavage with EcoRI also have approximately 1/10th the infectivity of supercoiled form I SV40 DNA (e.g., page 22.2f). Berg hypothesized this residual infectivity of SV40(LRI) DNA might be due to circles remaining in the DNA preps. However, no matter how much I enriched the DNA preps for linear SV40 DNA, this level of infectivity remained. Furthermore, the resulting progeny had supercoiled DNA with an intact EcoRI site. Thus, I hypothesized that maybe EcoRI cleavage leaves cohesive ends that get ligated back together inside monkey cells as happens when linear phage λ DNA with cohesive ends infects E. coli.
This hypothesis was tested in Chapter 40 (box 1, folders 9-10). Amazingly, 98% of the EcoRI ends were joined when I incubated SV40(LRI) DNA at 15℃ with E. coli DNA ligase (obtained from Paul Modrich, a Biochemistry graduate student in I. Robert Lehman’s laboratory). Most of the products were monomer circles when examined by electron microscopy (EM) (page 40.4a). This ligated DNA had also regained its infectivity (page 40.4c).
Ronald W. Davis (a new Assistant Professor in the Biochemistry Department at the time) then provided his advanced knowledge of physical chemistry and EM to this project. By preparing the EcoRI-linearized DNA for EM using a non-denaturing aqueous method, he found that much of it was circular even without ligase when spread in the cold room (page 40.4b)! He determined that the melting temperature of these cohesive ends was about 6℃ by spreading the DNA at a variety of temperatures (see summary of Ron’s data on page located between 44.3k and 44.4a). This experiment proved that the ends left by EcoRI cleavage were, indeed, “sticky” ones that can anneal by hydrogen bonding at low temperatures. In addition to SV40, Ron examined likewise a plasmid DNA with about19 EcoRI sites. All the EcoRI-generated DNA fragments could form hydrogen-bonded circles when spread for EM at low temperature. Thus, he concluded that all EcoRI ends are identical and 4 or 6 bases in length. Very shortly thereafter, we informed Herb Boyer and Howard Goodman, Assistant Professors at UC-San Franscisco at that time, of this fact. They then used this information to confirm our finding by sequencing these ends (Hedgpeth, Goodman & Boyer, PNAS 69:3448-2, 1972). We delayed publication of our discovery so as not to scoop them given the Boyer laboratory had very generously provided us with their not-yet-described-in-the-literature EcoRI enzyme. Thus, our two articles appeared in the same issue of PNAS (see below).
In Chapter 44 (box 1, folder 11), I proceeded to employ this knowledge to easily make recombinants using EcoRI-cleaved SV40 and λdvgal120 DNA, the same types of DNAs Dave had used to successfully make his recombinants the previous October (or August?), but now I only needed 2 enzymes, not 6 (protocol outlined on page 44.1a; see also schematic on page located between 44.3k and 44.4a). I simply mixed the differently radioactively labeled EcoRI-linearized DNAs at high DNA concentration and incubated them together with E. coli DNA ligase at 15℃. As a control, I incubated them separately with ligase before mixing them together. SV40 and λdvgal120 band at different densities in CsCl gradients because they have different G-C contents. Most of the DNA appeared at an intermediate density when the two DNAs were mixed before adding ligase (pages 44.4f,i,j). EM confirmed that about 65% of the DNA mass averaged about 8 SV40s in length (Mertz & Davis, PNAS 69:3370-4, 1972). With λdvgal120 being twice the size of SV40, many of these oligomers likely consisted of two or more λdvgals joined to one or more SV40s, with some of them containing head-to-tail dimers of λdvgal with an intact λ O gene, a gene that was disrupted in Jackson’s recombinants. Thus, I probably could have successfully cloned these SV40-λdvgal120 recombinants in E. coli in June 1972, 6 months before Cohen & Boyer began their drug-resistance marker cloning experiments (Cohen et al., PNAS 70:3240-4, 1973). However, I didn’t proceed to clone them because Berg’s laboratory had agreed the previous fall to a self-imposed moratorium on doing this experiment until safety issues related to the cloning of oncogenes in E. coli could be decided by the larger scientific community. Instead, I spent the remainder of my time in Berg’s lab developing other methods for isolating and growing SV40 mutants directly in monkey cells (see below). I co-authored with Paul Berg in 2010 some personal reflections on the origins and emergence of recombinant DNA technology (Berg, P, & Mertz, J.E., Genetics 184:9-17, 2010).
Given my August 1971 finding that SV40(LRI) DNA was infectious, I was already thinking that EcoRI restriction enzyme may cleave DNA generating cohesive ends when Victoria Sgaramella arrived at Stanford University in September 1971 to work largely independently as a postdoctoral fellow in Joshua Lederberg’s lab in the Genetics Department. Previously, Sgaramella had worked in Ghoban Khorana’s lab at UW-Madison and MIT where he had discovered blunt-end ligation by T4 DNA ligase of small synthetic oligonucleotides (Sgaramella et al., PNAS 67:1468, 1970; Sgaramella & Khorana, PNAS 69:3389, 1972). Sgaramella often attended Berg lab group meetings and Biochemistry Department seminars. Through these mechanisms, he learned about our lab’s unpublished findings that EcoRI cleaved SV40 DNA once at a unique site to generate linear DNA molecules and SV40(LRI) DNA was infectious in monkey cells with the progeny being wild-type SV40(I) DNA. With this knowledge in hand, Sgaramella obtained SV40(LRI) DNA from Morrow and P22 DNA from Lobban. He then performed a series of experiments from fall 1971 through summer 1972 from which he concluded that these EcoRI-generated ends were, indeed, different in some unknown way from the blunt ones present on phage P22 DNA: (i) He could generate dimers and trimers of linear phage P22 DNA, but not SV40(LRI), with phage T4 DNA ligase; and (ii) He could not generate SV40-P22 recombinants using T4 DNA ligase. As one of his controls, Sgaramella confirmed my April 1972 finding that one could generate dimers and trimers of SV40 (LRI) DNA by incubation with E. coli DNA ligase. This research was published in the same issue of PNAS as the Mertz & Davis and Hedgpeth et al. papers (Sgaramella, PNAS 69:3389, 1972).
III. Development of methods for cloning, growing and characterizing SV40 mutants.
Given the moratorium prevented me from growing non-viable mutants of SV40 by cloning them in E. coli (that lasted until 1978!), most of my thesis research centered around the development of other methods for cloning, growing and characterizing SV40 mutants, especially naturally arising defective ones. This research was performed beginning in the spring of 1971 and continued throughout my 4 2/3rd years in Berg’s lab. These experiments begin in Chapter 18 (box 1, folder 4). They continue in Chapter 25 (box 1, folder 7), Chapter 34 (box 1, folder 8), Chapter 36 (box 1, folders 8-9), Chapter 40 (box 1, folders 9-10), Chapter 42 (box 2, folder 3), and most of the remainder of my lab notebook from my time in the Berg laboratory, i.e., Chapters 51-94. (Note: Ron Davis taught me and others in the department how to do DNA electron microscopy including heteroduplex mapping shortly after his arrival in January 1972. I used these methods extensively for my studies with defective SV40 genomes as well as the cohesive ends study described above). This research led to several additional first-author publications listed below, some data that appeared only in my PhD thesis (Mertz, J.E. Deletion Mutants of Simian Virus 40. PhD Thesis, 1975, Stanford University), and much data related to naturally arising and laboratory-generated defective SV40 genomes that was never published:
Mertz, J.E. & Berg, P. Defective simian virus 40 genomes: isolation and growth of individual clones. Virology 62:112-124, 1974.
Mertz, J.E. & Berg, P. Viable deletion mutants of simian virus 40: selective isolation by means of a restriction endonuclease from Hemophilus parainfluenzae. Proc Natl Acad Sci U S A. 71:4879-4883, 1974.
Mertz JE, Carbon J, Herzberg M, Davis RW, Berg P. Isolation and characterization of individual clones of simian virus 40 mutants containing deletions duplications and insertions in their DNA. Cold Spring Harb Symp Quant Biol. 39 Pt 1:69-84, 1975.
Mertz, J.E. A detailed genetic analysis of the late complementation groups of simian virus 40. Virology. 132:173-185, 1984.
These methods were then extensively employed by the Berg laboratory throughout the latter half of the 1970s to generate deletion mutants of SV40, construct recombinants in which SV40 served as the vector for expression of bacterial and mammalian genes in mammalian cells, and to clone and grow these mutants and recombinants directly in monkey cells until the NIH Guidelines were modified to permit them to be cloned and propagated in E. coli. Among the numerous published studies that used these methods were the following:
Goff, S.P. & Berg, P. Construction of hybrid viruses containing SV40 and lambda phage DNA segments and their propagation in cultured monkey cells. Cell 9:695-705, 1976.
Cole, C.N. et al., Physical and genetic characterization of deletion mutants of simian virus 40 constructed in vitro. J Virol 24:277-294, 1977.
Goff, S.P. & Berg, P. Construction, propagation and expression of simian virus 40 recombinant genomes containing the Escherichia coli gene for thymidine kinase and a Saccharomyces cerevisae gene for tyrosine transfer RNA. J Mol Biol. 133:359-383, 1979.
Mulligan, R.C. et al. Synthesis of rabbit beta-globin in cultured monkey kidney cells following infection with a SV40 beta-globin recombinant genome. Nature 277:108-114, 1979.
Mulligan, R.C. & Berg, P. Expression of a bacterial gene in mammalian cells. Science 209:1422-1427, 1980.
General Notes
Each of Dr. Mertz's notebooks contain a table of contents. The full table of contents has been transcribed here, along with the title of the folder where that chapter can be found.
1. Propagating Cells (1.3)
2. SV40 Plaque Assay (1.1, 1.3)
3. Prep. Of Virus, Virus DNA, and Purifications (1.3)
4. Cell Lines – History and Propagation (1.2, 1.3, 2.2)
5. Transformation Assay of SV40 with BALB/3T3 (1.3)
6. Transformation of BALB/3T3 with SV40 DNA (1.3)
7. SV40 DNA Plaque Assay (1.1)
8. Growth Curves of Cell Lines (1.3)
9. Getting Circular DNA into E. Coli Without Helper (1.1)
10. Using Radioactivity (1.3)
11. Sterilizing DNA (1.3)
12. Staining Cells (1.3)
13. Testing for PPLD (Mycoplasma) (1.3)
14. Agar Suspension Test for Transferred Cells (1.3)
15. Using Machines Around Lab, Running Gradients, etc. (1.3, 2.2, 2.3)
16. Microtechnologies for Virus and Cell Studies (1.3)
17. Purification Procedure and Infectivity of Different Forms of SV40 DNA (1.1)
18. Studies on Formation of Defective (Mini) SV40 (1.3)
19. Isolation and Characterization of λdvgal120 (866dv120) (1.1, 1.2)
20. Studies on Irreversibly Denaturing SV40 Form I DNA, ss/linears (1.2)
21. Getting λdvgal (λdv120) Back into E. Coli (2.1)
22. DNA Plaque Assays, cont. (2.1)
23. Electron Microscopy (3.1, 4.1)
24. Diphenylamine Reactions (2.1)
25. SV40 Defectives (2.3)
26. Percent of Cells Infectible by SV40 Virus or DNA as Measured by Infectious Centers (2.3)
28. Trying to Get Mammalian Cell Amber Suppression I (2.1, 2.2)
29. Getting Cell Line with [illegible] Colony Forming Ability Under Agar (2.3)
30. Growing Cells with Agarose, Plasma, etc. (2.3, 3.1)
31. Infectivity of Alkaline Denatured SV40 DNA (2.2)
32. Model E Ultracentrifuge (2.3)
33. SV40 Plaque Assays Using AGMK Cells (3.1)
34. Continuing Studies of SV40 Defectives (3.1)
35. Studies with F1-8 (3.1)
36. EM Studies on SV40 Defective DNA (3.1, 3.2)
37. Methods for Nicking Supercoiled DNA (3.2)
38. Denaturation and Renaturation of DNA for Heteroduplexes (3.2)
39. Initial Experiments with SV-L vs. SV-S (3.2, 9.1)
40. Infectivity of Defectives, cont. and RI Treated SV40 DNA (3.2, 3.3)
41. Histograms of DNA Samples – Curve Tracing Measurements (5.1)
42. Making Lots of Defective (MA134) SV40 Virus and DNA; Making Lots of Non-Defective (MA134) SV40 Virus and DNA (5.1)
43. Transformation of BALBC/3T3 Cells (4.1)
44. Making λdvgal-SV40 Hybrids with RI Linears and Ligase (4.1)
45. Polymerase Experiments on R1-Treated DNA (4.1)
46. Working with 32P-XTP’s (4.1, 4.2)
47. Infectivity of RI-Treated λdvgal DNA by [CA] Assay (4.2)
48. Proving RI Cleavage is Totally Reversible by E. Coli Ligase (4.2)
49. Making 32P-SV40 DNA (4.2)
50. Does RI Bind to SV40 DNA (4.2)
51. Mapping Deletions and Substitutions in SV40 17L (4.2, 5.1, 5.2)
52. Mapping Deletions and Substitutions in SV40 34L (4.2, 5.2)
53. What is the RI-Resistant SV40 DNA? (4.2)
54. Making More Passage 3 Defective (AGMK) SV40 DNA (4.3)
55. Minicircle DNA (4.3)
56. Can One Get Permissively Transformed Cells Using “Defective” SV40? (4.3)
57. Experiments with Permissively Transformed Cells – SV40 AGNK (4.3)
58. Virus Stocks and DNA Stocks of Mutants (4.3)
59. Purifying Cell DNA from Liver (4.3)
60. Mapping Deletions and Substitutions in SV40 27L DNA (5.2)
61. Passage 4(AGMK) Defective, Pass 5 (5.2, 5.3)
62. Preparation of α-32PdNTPs (5.3)
63. Heteroduplexing 71r DNA (5.3)
64. In vivo properties of RI resistant DNA (5.3)
65. Making Non-Defective SV40 DNA and Virus (5.3)
66. Experiments with J. Sambrooks H. parainfluenzae enzyme (6.1)
67. Generation of SV40 Defectives – Effect of MOI and Passage (6.1)
68. Nick Translation to Make 32P-SV40 DNA (6.1)
69. Cots with 71r and 92 32P Labeled DNA (6.1)
70. Purification of H. parainfluenzae [illegible] Enzyme (6.2)
71. Testing DNA Preps. With Hpa B (5.2, 6.2)
72. Heteroduplex Mapping of 71(RRI, LHpaB) (6.2, 8.1)
73. Experiments with 71(RHpaB) and 71(RRI) DNA (6.2, 7.1, 8.2)
74. Running DNA on Gels (Slab Gels – General) (6.2)
75. Experiments with Mixed Plaques – Procedure to Test Progeny in ts Plaque (6.3, 7.1, 8.1)
76. Trying to Grow and Purify Individual Plaques of Deletion and Substitution Mutants (6.3, 7.1)
77. Making Stocks of SV-S Defectives on CVIP Cells (6.3, 7.1, 8.1)
78. Do Doubly Transformed Cells Have Their Genomes Integrated in Tandem? (6.3, 7.1)
79. Does Linear SV40 DNA Express Any Gene Functions? (6.3)
80. Trying to Transform CVIP Cells with Defective SV40 (8.2)
81. History and Histograms of Cloned Deletion and Substitution Mutants (7.1, 7.2, 8.1, 8.2)
82. Heteroduplex Mapping of Cloned Del and Sub Mutants (7.2, 7.3, 10.1, 10.2)
83. History and Gels on Hpa II-Resistant Plaque Forms (7.3, 8.1, 8.2, 9.1)
84. Infectivity of SS Circular Data (7.3, 9.1)
85. Trying to Make Permissive SV40-Transformed AGMK Lines (8.2)
86. Permissiveness of SV40-AGMK Cell Lines? (8.2)
87. Physiological Studies with B Mutants (9.1, 10.2)
88. Analysis of SV40 Virion Proteins of Plaque-Size Mutants (9.1)
89. Isolation of RII-Deletion Mutants (9.1, 9.2, 10.2)
90. Do SV40 Mutants Interfere with W.T. Viral Growth (9.2)
91. Plaque Purifying Del-Mutants Lacking Tandem Duplications (9.2)
92. Isolation of SV-S Pass 4(CVIP) Defective Mutants (9.2)
93. Analyzing Complementation Groups of Deletion Mutants and Deletion Mapping of ts Mutants (9.2, 9.3)
94. What is Defect in Plaque-Morphology (Hpa II-Resistant Mutants)? (9.3, 10.3)
Preferred Citation
Series I: Laboratory Notebooks, 1970-1975. Janet E. Mertz Collection, Cold Spring Harbor Laboratory Archives Digital Repository. 97-1610046. Update 2025-03-24.
Credit Line
Courtesy of Cold Spring Harbor Laboratory Archives.
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