# prodeng me veg Th -S Sefergm X Tb tS ptr

 

Dear Lederberg,

Thank you for your letter of March 26,which rea-
ched me two days ago. I have sent a letter to Hayes,of which I
enclose 4 copy, because he might already have sent his paper 4 or

Lad send it very soon-to the editors of JGM ,and on fur-

tnoer delay publication on the same issue ma ecome impossible,
Thank you for your newsre origin of resistance; I hope the rpprint
will reach me in time.

Tne problem of F+ effect on segregation is fusci-
nating ,but rather difficult to explain on current hypotheses. I
have tested thek asymmetry of segregations, analogous to that =
described in my earlier letter, also in the reversed crosses (i.e.

¥ (LB, -S?sugars + x TLB,+sugars -, F+ x P- and F- x Fe) ; it is al-

most superimposable on the preceding one. F+ x F+ crosses are so-
mewhat intermediate ,occasionally with some bias in one or other
sense ( which may be in agreement with your scheme of relative
sexuality) i.e. resembling more one bdfian the other of the two
corresponding F+ x F- , F—- x F+ crosses. Reymuetry is also found
in DM x W 945, Ft x Fe and-P- x F+ 3; F+ x F+ intermediate. I
have found myself testing mentally the wildest hypotheses. It may
be that tne F+ parent contributes a "shorter" chromosome - but I
am now favoring the idea that the F+ "gamete" carries a single
strand, while the F- gamete carries more than one (polytenic or
multinuclear ?) and that crossing-over can happen repeatedly
before segregation. However,even if the system behaved as a mul-
tivealant, with a single round of crossing-over,it might explain
the elimination of the contribution from the F+ parent,subject to
the restrictions due to the markers. You are in a much better po-
sition witn Het,where no fixed markers need being employed. Could
the data obtained from the Het segregations be eaplained assuming
that fertilizatiog results from the union of a haploid (F+) gamete
with a polyploid (F-) one,aa tet a welhinld 5 fornd.

I have no new data on Hfr; 1 have never kes edt te.
nuated strains,but shall do so . I shall test more crosses Hfr x
x TLB|-F+ to see if the differences 1 have found in behaviour re-
appear ,and send you the relevant cultures,

Re iirs.Lederberg's question on NCTC 123 : it was
possible to grow 123 on minimal + methionine + lysine,and thus se-
lect a few auxotrophs (a leucineless,and a threonineless):additio—
nal sugar and virus markers were added . R mixture of the auxo-
trophs ,or the separate auxotrophs (on methionine + Lysine) gave
no colonies. It is a poor test,and,the relevant strains were lost.

ywe rboyey
2nd puge, 3/4/52

when 1 tried again in Milan to grow the original strain on MLy, 1 cauld
never get any growth out of it. Almost all derivatives of 123 were lost
tn-tre when = moved from Cambridge to vtilan .1P8 is a voor grower; it
may have been lost/a “fhe Sritish .CTC - at least thus told me Weigle.
I am very glad to hear that irs,Lederberg has succeeded in doing some—
thing out of it ; li, have felt bitter against this strain for some time;
and&x am anxious/1? Q 3 can confirm my rather scanty experience about
its se#f-incompatibility .I never succeeded in getting prototrophs out
of it. bo they keep the original small colony CERES ° interesting
remark about colony size is tnat whiles all E&exazanks from 123 x bm
Nfr were small-sized, there was a segregation for size when crossing
123 to afr.

I shall let you have as soon as written ,the snort paper for
toe local iticrobiology congress,which I shall be glad to give an a joint
paper with the Lederbergs. I hope you can manage reading Italian ; it
may amuse you,for once, to try and understand it

Yours sincerely

CavaLk-