Macromolecular syntheses in the initiation of bacteriophage P1 induction

Abstract

The requirement for macromolecular syntheses in the initiation of the change from the lysogenic state to the lytic cycle has been studied in thymine-requiring Escherichia coli B3(P1b) under a variety of conditions which alter protein, ribosomal RNA and DNA synthesis. Thymine deprivation results in phage induction and in immediate inhibition of DNA synthesis (to 12 to 24% of normal). 5-Bromouracil replacing thymine in the medium gives induction as in the thymineless cultures, but with uninterrupted (70% or more of normal) DNA synthesis. Induction occurs, although at a slower rate, after a shift-down of the bacteria from broth to thymineless, minimalm edium, under which condition transient inhibition of protein and ribosomal-RNA synthesis occurs. Addition of 5-bromouracil after the shift-down results in increased DNA synthesis and accelerated induction. RNA and protein synthesis are inhibited longer than in the cultures without 5-bromouracil; induction reaches its maximum, in this case, before the RNA synthesis is resumed. Mitomycin C treatment of thymineless cultures shows an additive effect on induced cell formation, but no discernible effect on the interruption of DNA synthesis. The independence of induction of the effects on net synthesis of ribosomal RNA and protein and the correlation with alterations in DNA synthesis suggest the formation of an aberrant DNA as a triggering event in prophage induction.