Defective assembly of ribonucleic acid polymerase subunits in a temperature-sensitive .alpha.-subunit mutant of Escherichia coli

Publisher Website
Google Scholar
Abstract
The subunit assembly of RNA polymerase was investigated for the temperature-sensitive Escherichia coli strains carrying the mutation rpoA101 or rpoA112 in the gene encoding its .alpha. subunit. In cells carrying rpoA112, the sequential asembly of enzyme subunits is blocked at an early step, i.e., either the dimerization of altered .alpha. subunit or the subsequent association of altered .alpha. dimer with .beta. subunit. The unassembled free .alpha. subunit accumulates and the unassembled .beta. and .beta.'' subunits are degraded rapidly, in particular at a nonpermissive temperature. The assembly defect is accompanied by an overproduction of enzyme subunits apparently due to the decrease in the concentration of repressor holoenzyme involved in the autogenous regulation. The temperature-sensitive growth of rpoA112 mutants is attributed to the assembly defect of RNA polymerase as well as to the thermolability of asembled polymerase. The altered .alpha. subunit in a mutant carrying rpoA101 is assembled into the polymerase structure as efficiently as in wild-type cells; nevertheless, both .beta. and .beta.'' subunits are rapidly degraded in this mutant. The mutant polymerase is probably structurally different from the metabolically stable wild-type enzyme. Thus, the ts character of rpoA101 mutant is explained by the alteration in the structure and function of assembled RNA polymerase.