January 4, 1965
Dear Paul:
As you probably know, while he was in my lab last year, Mike Spencer found that the crystallisable yeast RNA which had been studied by the London group was in fact fragments of ribosomal RNA, rather than transfer RNA.  This may be interesting for ribosomology, but puts us back to square one as far as transfer RNA is concerned.
It is clear that we really need crystals of a pure species of transfer RNA (at least, pure enough to enable it to crystallise), yet as soon as I mention the quantities needed for preliminary X-ray work (about 100 mg), countercurrent men just keel over.  However, when I was last at Stanford I remember you were playing with a huge column for transfer RNA purification, and I wonder how this has developed.  Is it possible to get this kind of quantity of a "pure" transfer RNA?
We are getting still better pictures from fibers of double helical RNA (reo and MS2 "replicative form") which are now about as good as DNA.  But crystals are the ultimate.
I look forward to hearing from you.  Please give my regards to everyone.
With best wishes,
Sincerely,
Bob
P.S.  Your lecture here was excellent.