.

Department of Genetics
University of Wisconsin
Madison, Wisconsin

June 28, 1949

AI9 MAIL
--

Dear Cavallf :

Ym informative letter just received.

Enclosed find an aypm?.i~ with a summary of my data on the cross of S&i61

with W-585.  I 8m pleased that we should have made so nearly the, came obsel-va-

tione on the linkage relationships of Ma1 and Gal.  I don't ze(a how Ma1 eaz~ be

put on ths ma? at all!  Once I thought that it d&t be between B and 14 (which

would ma& any linkage either to Lac or to Bl, but this has been e%otded by

crosses in which both biotin and thiaine were added to the medium.  N- is

exceedingly stable, ao that it is possible to use it alone.  If Mai were be-

tween M and 31, it should car&uainly interact much more etrongly than it does

with 31.  It cannot be t-o theleft of Bl as it shows a closer linkage, wi+A BM,
and does not interact strongly with %. ff Ma1 ia in linear order,. on8 would        .

have to Flace it not far from 31, aad aaeme a non-random distribution of

crossing over.  I would rather relate Nal ptjculiarities to the fact that it is

almost illvariably hemizygons izx ths heteronygotes.  If the zygotes from klliich
prototroshs are isolated are comparable (except for persistence) to the hetero-

zygotez, then on8 wdd get an qparent linkage based on the fact that in some

way Mati is almost always lost! The 8ame probably appi&e to Gal. I've just

completed some reversion experiments on Gal- heteroaygotes which show that Gal

is also hemizygous.  Howeme, whereas the heterozygotes (from a cross involving

W-583) are almost invariably Mal- (hemizygous Mal-), many of them are either Gal-

or Gai#.  The Gal factor of W-583 has never been obaerved heterozygons, end only
recently I have found the first instance of a Ma1 heterozygote.  Heterozygositg
    .


                                                            4y _.., _._ -I'
PZLge2- June 28, 1949

for Ma1 is certainly very rare indeed, e.nd possibly may arise from quite a dif-
ferent meahanism than the other aneuploid heterozygotee. I really still do not

have a good story on the mechanisms of this heterozygote, but thfa summ8r for-

tUXb8iy, I have a good deal Of assistanae, and am approaahing the problem on

a zuitably large scale.  We need mostly some good information on the inheritance
of a, but ao far only the A, B, and (1 stocks mentioned in ~qg paper haye carried

it.

  In your letter you refer to the possibility of oonfusion based on the epistasis
         . .
of Gal,+ to Lac-.  I wonder if you do not kve a typographical.error. If Gal$ were

epistatic, then the standard Lac- stocks (e.g. Y-53 or T-87) could not be recoe

nized as such, since they are Gal&.  Gal- ia aepistatfcff to La#, in the sense

that it is sometimes difficult to soore a Gsl-Laci) as Lae#, i.e., the Gal-

weakans the iaetose fermentation.
              

I must certainly agrse with you about the difficulty of scoring Are.  I

hW8 not used it to any extant.  IC, seems to be almost completely linked to Gal.

I was interested ia'your observation abxt tixed prototroph eolo.nies.  I have

seen them ra Lao, espeoially by conducti% the crosses on synthetic EM3 lactose,

where they cm be seeu diractly as colonies with integral sectors.  However, Ihad

the i~rassion that rather less than 15 of the colonies were mixad for tic.  On
kltose EMS, more than 105 of the (few) IJal# prototrophs also have a Xk- sector.

I have thought of these as likely to be sister neiotic products, because thera
ara distinct correlations in their Lac aad ? segrsgations which one would not

eqect from dlstinut zygotes.

  On the other hand, f think there is a good prima facie case that the mixed
prototrophs you get from year Hfr crosses are likely to some iron several zygotes.
                                                               \I

You point out yourself the extent of microcolony formation.  If the rate of recoz-
      .                                                     .
- bination is high, one would have to &ect that several cells from a microcolony

at a &Yen p&u?8 till each paSticipat8 in a fusion and produce Several zygOt8s.


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a9e3- June 28.1949

.

siZkCe YOU &VS SOm8 hint Or an f-1 test Of wr, I assume thrrt you hzve succeeded

  I

in recovering mnlfiple mutant as well as prototrqh reaombinants with its help. As

you may imagine, I am~exceedingly interested in t:lis atock, and would like verymuch
to have the -portunity of confirming your observations. you aan be sure that ycm

will be kgt fully informed of any ffndings, and that we will. make no attempt to
intrude on any area in which you would be particularly interested.  If you agree

to send it, I: would be most appreciative.  However, r hope that this request vill

not em'oarrass you, as 1 can wei understti t-hat you might have some reticence
abmt distributing it so early in your investigation.  I gather that you are     . .
active4 pursuing the problem of the'mochanism whereby Hfr is-more active thsn

58-161 in producing prototrophs.  Have you considered the likelihood i&t it msy
                                                   
b8 mu& mars motile?  X have often thought that their tight be a chenotro$sn

between distinct mutants, for each pro&aces the needs of the other, and some

such Fhenomenon might dfs~30s8 of ths kinetic difficulties.
  Lately, I have realized that some of my stocks ax9 consistently Lfr (low
frequency of recombin.&ion) for no obvious biochemical reason.  This has been

particularly true of crosses of Lacp with Lz-, even on glucose medPxn on which
                                                     

either of them grow very well with proper supplements. I have iso noticed this

among a number of segrsgants from H- stocks, agailrlth no obvious chenid basis.
f have hoped to use these &fr stocks t? 8XplOr8 enViroment83 COnditiOn_ -&i.zh

might sti;rmlate recombination, thinIcing that the "standards rate was naarly all
                         .

one 0ouI.d expect onkinetic grounds.  I will be glad to sand you some of these

if they would help your analysfs.                                     .

Secondly, one of the most prqmisl~lp, leads ia the investigation of the hetem-
zygotes has been the finding &at some segregants give markew altered ratios cf
            

Iad and Ma19 protokrophs (both graatljr inoreaS8d) compsred to biochemically ocst-
                                                          
parable stocks. !Chis tends to support the notion that a chromosonal. aberration

is involved, but is still faz from definitive.
.

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wize4- June 28.1949

  With all of the confusion uonaerning the linkages of Gal and Mal, I wonder

whether you may not be very acetical abont linearity.  Certainly 1 would bel
However, mag I suggest that you sometime tq the V6-Lac-Vl series mentioned          /-

in npr Genetics paper which gave quite cleancut results.

Yours very sincerely,

Joshua Lederberg

/w

P.S.  on looking over my notes, -X flnd,that X cannot give you any worthwhile
account of the crosses.1 did with 58-161 x W583.  1 noticed that there were very

few Gal# Law or Gal- La&, but decided that I couMu*t score the latter at all.
Later I noticed that 35 lactose facili+Wxd scar%=, but X hamutt ussd this to

collect quautitative data.  Bowever, hers am some scores for maltose.aud galactose.


, ;         X-G#    !4$G-    wc#

   34      10      s       2      4 (0)
                              ExD. 353
   43     15 2       0     '1 (21)

when I realized that G-L# wa's diffi&lt to score, I abandoned W533 and used ~677
which has the other disadvanta&e that Gal itself is difficult to read. f sm
tr&g to per?ect better stocks.  These data certainly put Gal and Mal rather
far wart, and I still wonder whether && lsa*t mar Lac, as you bdicate.
Your data show ab%xt $ triples.  This & disturbingly high (like table 6

in my Genetics paper) but it seems to be so!