16/2/52 Dre Hayes Depteof Bacteriology Postgraduate ‘edical School Ducane Rd. Lond onn W212 Dear Hayes, Thank you for your letter of Feb.l0th and the enclosed note to Neture 3; I ar interested to see that UV astinulation agrees with,and erhans follows fron,Pfertility behaviour, i have a strain with a higher frequency of recor bi~ nation that seers to have a hivrher sensitivity to UV stimulae tion than 3 ~161 (fron which it was derived). Am to Syicer's infertile strain -~ 7 think he sent ne a subculture of it sone bi:e ago; I can reoall writing hin s:nething about infer\ili-e ty of one of his strains ~ it is probadly the fomrth occurren— ce of the sare event, viz.muteation to infertility.%he first rust have been in the buildins of TLB,- 3 one ocourred in a Bow strain -hich I treated with Ny in 19493 another to rs, Lederberg again ina Bie strain. I have a subculture of this, which was sent te ne by Lederber:, Re your experiuents: I think I een oredict tre result ofx the experinent which you plan,of infectin, an infertile strain with a fer'ile one.it was discovered by Le~ derber; a month ago,and 1 was reaching when I heard of it,e- xaotly the sane conclusion ,that fertility(rethertself—ferti-~ lity) is infective. It is very highly infective. In 4 hours consaot(shorter ¢xposures not tested) 90. of the cells of en infer:ile strain are infected. It is +ot easy to detabh the transformins principle off the fertile cella: I hove how~ ever to confir: sore e&perinents which were vositive recently. Infection is rore difficult in the presence of DNA-ase 3; ard is enhanced by UVe-stimulation,so ‘hat_it may well be that the tranaforrning orineiple be the sane SHReeeBSe your irradiae ted cultures viscid. However,ihe transforminz principle mus‘ b . be either insohuble or highly unstable in sOlution,since £4 caniot be recovered easily in filtrates, . When I suggested crossing two streptowyoinasterilised strains to-ether, I meant sf course using two fertile straina. I have some idea tha’: sometes -if there are any such things — may be formed on both sides. On the present evidence,it may be that the tufarkiltity