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Abstract

DNA synthesis was studied in endonuclease I (endI)-deficient mutant cells, made permeable to nucleotides by a short treatment with ether. DNA synthesis in the non-viable cells depends on external supply of the four deoxynucleoside triphosphates; it occurs also in a deoxynucleoside monophosphate-ATP mixture and is independent of exogenous template. The product is autoradiographically associated with cells and homogeneously distributed within a population. DNA synthesis is independent of a polA+ (DNA polymerase) gene, suppressed by pretreatment with mitomycin C, reactivated by subsequent infection with bacteriophage φX174 and, on the basis of these criteria, resembles DNA synthesis in vivo. DNA synthesis is suppressed also by a mercurial. Ultrasonication or endonucleolytic activity provokes additional DNA-synthesizing activity which is not suppressed by mitomycin or a mercurial, and detectable only in polA+ cells. The extent of inhibition achieved with mitomycin in polA+ cells is taken to indicate that ether-treated cells contain unfragmented DNA under normal assay conditions.