15 
(Georgopoulos , 1971) has been introduced into \1776, or since 7N mutants 
are by nature leaky, there is "no suppressor present and these results 
are due to leakiness. The proper assay for the presence of the sup E42 
allele would be to ask for suppression of an amber (e.g., I plac Z ^ in a 
lac background) whose gene expression can be assayed directly. 
§6. The thyA 57 allele was found to revert in yX778> which does not 
occur in all other strains tested for reversion of thyA 57 . It is not 
clear whether the thyA 57 allele is the marker present in y$-776 conveying 
the thy phenotype, since no control cotransduction marker was used in 
its introduction (see this paper, §4). 
§7. The uncharacterized rfb-2 mutation (see this paper, §2c) 
reverts at a low frequency. However, since this allele confers a multiple 
phenotype on Xl?76 (sensitivity to bile salts, detergents, antibiotics, 
and drugs; conjugation deficiency; and partial resistance to phage PI), 
Curtiss £t^ a_l . (p.ll) conclude that revertants of this allele "have 
numerous associated changes, that in some respects compromise the safety 
of yl776 and X1876." 
Phenotypic characterization : 
§8. DAP-less death: 
a) DAP-less death for X^76 proceeds more rapidly in conditions 
under which cells can carry out macromolecular synthesis than in more 
minimal starvation media (e.g., BSG, distilled water, tap water). This 
indicates that the strain is more likely to survive in poorer (natural 
"famine") environments than in richer (laboratory) environments. 
b) "DAP-less death curves for ~)(187 6 indicate that a culture 
undergoing death contains two populations of cells, one of which dies 
(Appendix C — 203] 
