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.     

Nucleotide and deduced amino acid sequence of the gene for a novel protein with a possible regulatory function encoded in the β operon of Staphylococcus aureus

Abstract Although considerable homology exists between the translation products of the rplL, rpoB and rpoC genes of the β operons of the Gram-negative organism Escherichia coli and the Gram-positive Staphylococcus aureus the region between the rplL and rpoB genes is quite different in the two bacterial species. In E. coli the 324 bp has three centres of dyad symmetry in the first half of the sequence and multiple nonsense codons in all three reading frames. By contrast, the corresponding region in S. aureus consists of 1000 bp capable of forming a similar arrangement of stem-loop structures but with an open reading frame, sited 177 bp downstream of the end of rplL and 217 bp upstream of the beginning of the rpoB gene, with consensus initiation and termination signals, which if translated would generate a 22,665 Da protein with 202 amino acids. In view of the inability to find any significant homology with other proteins in the data bank and because the evidence suggests, as in E. coli , that the rplL-rpoB intergenic sequence is involved in regulation it is proposed that the expression product of orf202 may be a further element of control in the S. aureus β operon.     

Escherichia coli ribosomal protein L10 is rapidly degraded when synthesized in excess of ribosomal protein L7/L12.

In Escherichia coli the genes encoding ribosomal proteins L10 and L7/12, rplJ and rplL, respectively, are cotranscribed and subject to translational coupling. Synthesis of both proteins is coordinately regulated at the translational level by binding of L10 or a complex of L10 and L7/L12 to a single target in the mRNA leader region upstream of rplJ. Unexpectedly, small deletions that inactivated the ribosome-binding site of the rplL gene carried on multicopy plasmids exerted a negative effect on expression of the upstream rplJ gene. This effect could be overcome by overproduction of L7/L12 in trans from another plasmid. This apparent stimulation resulted from stabilization of the overproduced L10 protein by L7/L12, presumably because free L10, in contrast to L10 complexed with L7/L12, is subject to rapid proteolytic decay. The contribution of this decay mechanism to the regulation of the rplJL operon is evaluated.