March 14, 1972
Dear Dan,
Ernest and I are very grateful to you and Kathy Danna for sending the H. influenzae restriction enzyme as well as instructions. Gary Felsenfeld was a good courier -- bringing also some RNase II from my lab for Uri Littauer. The endonuclease arrived in good condition. Scaling down the amount recommended by Kathy for 50 [micro]grams of SV40 DNA, we got complete conversion of 1 [micro]gram to 7S material by 0.2 [micro]liter. We're proceeding now with the gels and will keep in touch with you concerning hybridization results if and when we get them. I am also planning on trying again with an enzyme preparation so as to be able to leave Ernest with a good supply before I leave next summer. This time I will set up a proper assay.
We now have several separate isolates of high passage stocks, each starting with a different clone. Each clone finally yields a stock with a different characteristic amount of homology to BSC DNA. Happily, repassage of the same clones leads to the same result each time, so perhaps we are dealing with something more reproducible than simple chance. The endonuclease should be a further help sorting this out.
Congratulations on becoming chairman of the Microbiology Department. But don't let it keep you from Israel for too long. At this stage we're not at all sure we'll ever get our kids back to Washington. The whole family is having a wonderful time.
Thanks again and best regards,
Sincerely yours,
Maxine Singer.