21.prf February 3.967,

Dr s. OChQEf,
Departmant sf 3ioehe?mistry,
Flew York University School of B!edicln%,
550 Iti.rst Avenue,
New York X6,
U.S.A.

    Thank you for your letter of 13th February,   Wc9 were very interested
to learn that UGA gives negative results w%th both tryptoghan and cystelns.
Our present id%a for the end and betinning of clstrons is UAAUCA, it bejing
assurnsd that the n%w cfstron atarta wnZth tha AUG read out of phase,   We
would only expect this to occur between cIstrons whioh were read with

*  equal efficiency,

   We were alao fnterestcs3 to hear that you can produce formyl.met-phe
in good yi%lds in th% c%ll-fP%% sy8t8m4   Mark Bretscher had tried AUGUAA
in the hope that it wound raleasa formylmethionine, but it only did so
extremely poorly.   More recently he has been working with the amber
fragmsnt at the b%ginnjin& of $2,   However we have sc far been quite
unsuccessful In fitndlng the hypothetical chafn tarmfnating tRNA, and
wPl1 be interested to learn whether you have had any better luck than
we have,

   We should all b8 del5ghtsd to see you here in April,   Either th%
27th or the 28th would be equally convenient.   Perhaps you would let
me know nearer the da-t% wh%ch day you prefer and whether you would lfke
us to ma&s a hotel reservatfon for youI   X do not know v&&hey you
would car% tt;o &v% us $ farmaZ talk, but '~91% would bs quJtte happy far
you to chat to us inf~rmaI.3.y if you would prefer that,      .
                    @%

  Apar% f"rorn the work on UGA the,important ram&t we have hare is
that the alteratitm to ths tyrosine ~tu  tZWA is the sxpeoted on% in the
antfcodon.   We ar% hoping to piok up other mutants in tkfs partioular


-2-

Dr S. Ochoa,

2192; Pebruarg 196,7p

tRl?A but the work h&B- only just got under way 80 we havs na more
results yet.

,, Greatly looking forward to your vi&t,

F,H,C, CrSak,

.