November 2, 1956

Dear Dr. Mitchell:

Ui want to thank you for the "shower of reprints and mss." you have
taken the trouble to send oe. I an greatly interested in your approach
to many problems of common interest, and this material makes it much
easier to catch up on background reading.

I had two reagons last Spring (18. just before the Bect. inatony
Symposium) for following up the hunch that L-forms and protoplasts
might be related: a) the hops of clearing up the biological sigaificance
of a very mrky subject, and b) the hope that protoplasts might be used
very effectively in genetic—physiological investigation. Professor Spiegel-
man has been exploiting ome aspects/of the latter, with very encouraging
results, i.6., in demonstrating “aynpoietic’ effects of RNA from Lac+
strains in provoking lactase synthesis in protoplast preparations of
verious Luc- amatants. I had hoped we could ake similar trials with
DNA in transduction experiments, but these have so far failed: the problem
may be to create a systen which is sufficiently periusuble to DNA and staéll
viable (1.e. capable of clonal growth). Clearly there ure innumerable ways
to try such experiments, and we are contiauing with than. Uafortunately,
thers is no authentic report of DNA-transduction in genetically favorable
strains of enteric bacteria.

it hac occurred to ae that the paasic changes in pneumecoceid which
underly their ‘competence te as recipients in transformation (ef. Hoteh-
iss, Proc Kat Acad Sel 40:49, 1954) might be rclated to « stretching
of the cell wall— which must be very closes to what you have in mind
in youb letter and discussion in the &.A. Symposium. Would it be possible
te encourage you to investigate pneumococci from this point of view,
by your biophysical techniques? ‘this is almost a unique system where the
uptake of DNA can be demonstmted, and it has not been weil defined at
ail us a biophysieai problem.

Penicillin-induced protoplasts ani L-colonies have retained their
F+ quality and, in large measure their ability to mate. However, the proto-
plasts may not be completely denuded: for example they show a prominent
capsule in india-ink preparations. The capsule is invisible in phase-contrast
jwhether it represehts the remains of the wall of an augmentation of the
normal K- antigen has to be determined, vrobably by Tomscik's methods. I
am not clearf whether other authors have studied protoplasts in this fashion,
but am suspicious that some of the "haloes" in published photographs may
2@ more than the usual phase-optical artefact. If the wall-constituents
are partly retained, it may explain why we have mot yet obtained irreversible
L colony types (accepting the primer hypothesis, which is one of several
possibilities),

I am hopeful of visiting Edinburgh next March, and of taking advant
of the occasion to discuss these questions at first hand. Professor V
dington should be cognizant of these plans.

Yours sincerely,