November 29, 1972 Dear Kathy: I was pleased to hear that you are enjoying Gent and are making progress on the fragments. I am working on the preparation of restriction enzymes myself, starting with H. influenzae enzyme. It looks as though we have the second enzyme (complementary to Ham's fraction) which gives A, E, K plus partials. We intend to grow H. parainfluenzae, H. aegyptius and E. coli (RTF2) next week in the NIH 300-liter fermenter. I (or George) plan to prepare large batches of these enzymes and will send you some of each. Your paper is now complete and will go off to JMB this week. George did get cleavage of C by Hpa enzyme, identifying both products and also cleavage of F by Hin with both products identified. It looks very good; I'll be sending you a copy of the submitted manuscript. The work on defectives is going nicely. Theresa has hybridized fragments of P13 and P20 to SV40 DNA and to BSC1 DNA and can detect fragments with only unique BSC DNA or with reiterated BSC DNA, SV40 DNA, or both. We intend to map some of these. I am about to write the letter to the Wilson S. Stone Memorial Award Committee in support of your application. If the judges are discerning, they'll give you the money. With best regards to Walter Fiers, to whom I am also writing, Sincerely, Daniel Nathans