Original Repository: Alan Mason Chesney Medical Archives. Daniel Nathans Collection
Reproduced with permission of Joanne Nathans.
Restriction Enzymes and the "New Genetics," 1970-1980
Letter from Paul Berg to Daniel Nathans (September 9, 1976)
September 20, 1976
I am sending separately the following materials you requested:
SV40: dl-1001, 1002, 1009
Cells: Balb/c 3T3
dl-1001 is a stable mutant, but 1002 and 1009 have repeatedly given other variants when cloned and propagated. dl-1002 DNA
can be readily purified by gel electrophoresis; dl-1009 DNA, with more difficulty, and we have therefore not done anything
with it. All of these were cloned with tsB helper. To make stocks we apply 0.2 ml of a 1:10 dilution of original stock (made
from a plaque suspension) to the edge of a 10-cm cell monolayer, let virus absorb 37 degrees for 60', and incubate at
40 degrees until lysis.
Balb/c 3T3 cells came from George Todaro in December, 1974, as his A31 subclone 7, the most contact-inhibited clone he had.
Still one gets spontaneous transformants when these cells are passed for any length of time. I suggest you freeze down an
early passage and of course check what you grow for spontaneous morphologic transformation. We noticed that SV40 transformants
of Balb/c 3T3 are much denser than spontaneous ones and all colonies of this type we tested (about two dozen) had SV40 T antigen.
I have also used secondary CHL cells (Chinese hamster lung cells) obtained from Bob Martin and Janice Chou. SV40 transformants
were easy to score, and the cells could be transformed by SV40 DNA. We have not tried rat cells.
The enclosed table gives results of transformation of CHL and Balb/c 3T3 cells by SV40 DNA with Graham and van der Eb's
procedure. We have not had a great deal of experience with the DNA transformations, and specifically we have not varied conditions
(for example, plating smaller numbers of infected cells) to see if we could get a more linear dose response.
In regard to dl-1003, missing Hin-E, Ching-Juh Lai found that it does not complement tsB, C or D mutants (see his 1974 Cold
Spring Harbor paper and enclosed preprint), from which we inferred that Hin-E may have a transcriptional, processing, or translational
signal for expression of the B/C gene. Ching-Juh is now following this up with George Khoury along the lines you outlined
in your letter.
As far as our plans for early deletion mutants go, Stu Adler now has a fairly complete set, and he plans to test them for
biological properties, including early mRNA and T antigen protein. I think at the present stage our labs can't avoid overlaps
like this, since the mutants are mostly new, but I too hope we can exchange information and materials to cut down undesirable
duplication. I expect we'll be branching off in different directions before very long.
Thanks very much for the invitation to visit Stanford. I would like to come, but in the coming months I'll be away from
the lab a fair amount and am reluctant to increase the time away. Please give me a rain check.
Let me know if there is a problem with cells or virus when they arrive. I look forward to seeing you in Miami.