DOES REPLICATION-INDUCED TRANSCRIPTION REGULATE SYNTHESIS OF THE MYRIAD LOW COPY NUMBER PROTEINS OF ESCHERICHIA-COLI

Over 80% of the genes in the E. coli chromosome express fewer than a h undred copies each of their protein products per cell. it is argued he re that transcription of these genes is neither constitutive nor regul ated by protein factors, but rather, induced by the act of replication . The utility of such replication-induced (RI) transcription to the te mporal regulation of synthesis of determinate quantities of low copy n umber (LCN) proteins is described. It is suggested that RI transcripti on may be necessitated, as well as facilitated, by the folding of the bacterial chromosome into a compact nucleoid. Mechanistic aspects of t he induction of transcription by replication are discussed with respec t to the modulation of transcriptional initiation by negative supercoi ling effects, promoter methylation status and derepression. It is show n that RI transcription offers plausible explanations for the constanc y of the C period of the E. coli cell cycle and the remarkable conserv ation of gene order in the chromosomes of enteric bacteria. Some exper imental tests of the hypothesis are proposed.