The effect of gene dosage on the synthesis and stability of RNA polymerase subunits in Escherichia coli

Summary

We describe studies on the rate of synthesis and the stability of the β and β′ subunits of RNA polymerase, in various strains of E. coli. These include a normal haploid strain: diploid strains carrying a second copy of the rif operon (which codes for β and β′) on the F′-factor, KLF10: and rif ⁰_am /KLF10 rif ^R strains, in which the chromosomal rif (β) gene is inactivated by an unsuppressed amber mutation. We find that the normal diploid strains synthesise β and β′ at a higher rate than the parental haploid. Amber mutations in one of the rif copies cause a reduction in the rate of β synthesis. Amongst these, a polar mutation affecting both β and β′ synthesis has been tentatively identified. Whereas the β and β′ subunits synthesised in haploids are stable, the extra quantities of β and β′ synthesised by the KLF10 merodiploid derivatives are quite rapidly degraded.