NEW YORK UNIVERSITY MEDICAL CENTER
NEW YORK UNIVERSITY SCHOOL OF MEDICINE

5 50 FIRST AVENUE, NEW YORK 16. N.Y.

DEPARTMENT OF BIOCHEMISTRY

February 13, 1967

Dr. F. H. C. Crick
M. R. C. Laboratory of Molecular Biology
Hills Road

Cambridge, England

Dear Francis:

     We have been tickled by your recent paper in Nature on
UGA. We tried a few times whether this triplet would code for
anything with oligonucleotides of the type AAAUGAAAA. . .AAA and
got negative results with both tryptophan and cysteine. As you
may remember, the cell-free system misses the 5'-end triplet in
such polymers but translates the others. It would be interesting
if UGA indeed functions as a spacer triplet between genes. In
some of my lectures I have been writing UAAAUG for the end and
beginning of cistrons, respectively. Do you think it is going to
be UAAUGAAUG?

    We have now good evidence that, upon translation of
MS2 RNA by the E. coli system, both the coat protein and the syn-
thetase are initiated with formylmethionine. We do not get intact
maturation factor protein in vitro, probably because of nucleases
in the system.  We also have final proof for UAA as a chain ter-
mination codon.  On translation of polymers of the type AUGUUU
UAAAAA.. .AAA, the cell-free system forms formylmet-phe in good
yields, as the free dipeptide released in the supernatant.

OREGON g-3200

     I am going to be in western Europe this spring and I am
planning to visit England the last week in April.  I would of course


like to take this opportunity to spend a day in Cambridge. Would
April 27 or 28 be convenient?

With best regards,\ as always

Yours,

Sever0 Ochoa

.