Dr, F,H,C, Crick,
Cavendish Laboratory,
Free Sohaol. Lane,
C-IDW.

6th June, 19fiSI

Dear Francis,

Many tha-rlks for yotzr letter and comments,

     The "close approximation to threen seem to be a
definite stereoshemica1 requirement, although the fact that
the requirement corresponds closely to a small whole mber
may be fortuitous.
obtained with ScWammb pdymerisecl A - protein.  This gives
diagrams as spotty as TMV b  the maxima on layer-rims 3
etc. appear to be truly ax&. This X take to mean that the
stuff is a pile of discs  thickness 23 A, each containing 12
units (if it is 12) in piaoe of the 129 per turn of the helix,
and each rotated with respect to its neighbour above and below
by an amount corresponding to one third of a unit,  I enOlOS8
a print of a bad A-protein photo - I have recently gat better
ones.

3 say this on the basis of results recently

6,

As for potato X, I have always intended to work on

it as soon a8 1 can get hold of same. I haV8 asked bothRoy
and Plrie for It, but gat no answer from either,
gestion 3[ shall now writs agaPn to Ray.
best, now, to start work on it in the autumn, when I shall have
two new people here to share the vork,

                                                but
has not given the reasons why he rejected other possible sign
oombinatima. He is codng over here some time In the summer
and wrqnter to work here for a while.

At yous sug-

Xt would probably be

Caspar has written to me at length about his work

I expect you have heard from Alex that ha now intends
over at the beginning of July and stay about 6 wmks -

to
presumably golag to Brussels.

I am beginning to think that the groove is due  to a

helical array of knobs rather than to a continuous helical ridge,

It Wit11 be nice to be able to discuss all theso things
     I hope we shall all be able to get together

again with Jim.
some tine before Br~SS8br