Evidence for co-transcription of the RNA polymerase genes rpoBC with a ribosomal protein gene of escherichia coli.

The adjacent genes rpoB and rpoC code for the beta and beta' subunits of RNA polymerase in Escherichia coli, and are cotranscribed in the order given. The nearest known genes to rpoB are rplL and rplA,J,K, which code for ribosomal proteins, and which are transcribed in the same direction as the polymerase genes. It has been suggested that rpoBC may be distal elements of a larger operon including these ribosomal genes. To test this possibility we have cloned a segment of DNA, derived by endoR. HindIII digestion from the rpoBC-transducing bacteriophage lambdarifd18, in the replacement vector NMlambda761. The structure of the lambdarpoBC bacteriophages so produced is such that the inserted DNA can be transcribed from lambda promoters, allowing us to confirm that it carries intact rplL, rpoB, and rpoC genes. We have studied these bacteriophages as lysogens in rec+ and rec bacteria, and by infection of UV-irradiated bacterial strains in which lambda promoters are either repressed or active. The results indicate that the cloned DNA contains at most a very weak promoter for the above genes, in contrast to that present in the larger segment of bacterial DNA carried by lambdarifd18. We have in the same way cloned the adjacent bacterial HindIII-fragment of lambdarifd18 DNA, and have found that it displays vigorous autonomous expression of the tufB, rplA, and rplK genes. We conclude that rpoB and C are obligatorily co-transcribed with rplL, from a promoter located outside the DNA segment cloned in lambdarpoBC. We discuss the evidence for the existence of a regulatory site, rpoU, located between rplL and rpoB.

Loss of the sigma activity of RNA polymerase of Bacillus subtilis during sporulation.

The activity of the sigma subunit of the RNA polymerase of Bacillus subtilis decreases markedly during the first 2 hr of sporulation. Moreover, sigma activity remains deficient throughout the sporulation process and in dormant spores. The time course of changes in RNA polymerase during sporulation indicates that alterations in the core of RNA polymerase occur after the loss of sigma activity. Core RNA polymerase purified after the second and before the ninth hour of sporulation fails to respond to vegetative sigma subunit in vitro and contains variable amounts of a 110,000-dalton polypeptide in place of the beta' subunit. Core RNA polymerase purified from dormant spores has a subunit structure indistinguishable from vegetative core enzyme.RNA polymerase purified by antibody precipitation from an extract of a mixture of sporulating and excess vegetative cells separately labeled with two different radioisotopes contains beta' subunit and no 110,000-dalton polypeptide. However, RNA polymerase purified from sporulating bacteria in the absence of excess vegetative cells progressively loses the beta' subunit at each stage of purification even in the presence of the protease inhibitor, phenylmethyl sulfonyl fluoride. These findings suggest that the alteration of the beta' subunit is due to proteolysis in vitro.

Isolation of a new RNA polymerase-binding protein from sporulating Bacillus subtilis.

RNA polymerase was precipitated from extracts of radioactively labeled vegetative and sporulating Bacillus subtilis with antiserum prepared against vegetative core polymerase. The precipitates were solubilized and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Antiserum added to an extract of vegetative B. subtilis precipitated only the known subunits of core RNA polymerase, but antiserum added to an extract of sporulating cells precipitated a new polypeptide of 70,000 daltons in addition to the subunits of core enzyme. The 70,000-dalton polypeptide precipitated from an extract of a mixture of vegetative and sporulating B. subtilis, separately labeled with two different radioisotopes, contained only the radioisotope characteristic of the sporulating cells. The 70,000-dalton protein has been freed of core RNA polymerase and extensively purified by chromatography on phosphocellulose. Precipitation of the purified 70,000-dalton protein by the anti-polymerase serum requires the prior addition of vegetative or sporulation core RNA polymerase. The reaction is specific since the purified protein is not precipitated during antibody precipitation of either phage lambda repressor or bovine serum albumin. The RNA polymerase-binding protein appears during the third hour of sporulation and is apparently not synthesized by the sporulation-defective mutant rfr 10.