Genetic implications of periodic pulsations of the rate of synthesis and the composition of rapidly labeled bacterial RNA.

Abstract

When synchronous cultures of a donor strain of E. coli K12 are subjected to short pulses of P32 -orthophosphate at regular intervals, a rhythmic pattern of the rate of synthesis and of the composition of rapidly labeled RNA is observed, with the RNA produced at the peak periods of P32 incorporation resembling ribosomal RNA in composition. In the previously investigated strain HfrH, two peaks occurred in each growth cycle coincident with the replication of DNA by 40 to 80 per cent. A very similar pattern has been found now in an organism having a different chromosomal polarity, namely, E. coli AB312; but this time the rate bursts, accompanied by compositional shifts, occurred at the beginning of the replicative cycle and when 60 per cent of the DNA had duplicated. These findings permit a correlation witn the genetic map of E. coli K12 and lead to the conclusion that in both strains one RNA peak is very close to the streptomycin locus and the other between the loci for tryptophan and histidine.