DNA-dependent RNA polymerase from Pseudomonas BAL-31. Effect of sigma and template homology on the stimulation and selectivity of transcription

A bacteriophage T4 expression cassette that functions efficiently in a wide range of gram-negative bacteria

We have constructed a derivative of the broad-host-range vector RSF1010. This plasmid, p alpha omega, contains an expression cassette derived from bacteriophage T4 gene 32, into which we have inserted the coding sequence for the xylE enzyme (C2,3O) of the TOL plasmid pWWO. The composite plasmid, p alpha xylE omega, was transferred by conjugal mobilisation into a variety of Gram-negative bacteria (Agrobacter, Paracoccus, Erwinia, Pseudomonas, Rhizobium and Xanthomonas). High levels of C2,3O activity were found in almost all of the extracts. Polyacrylamide gel electrophoresis of these extracts revealed a prominent protein band at 35 kDa whose identity as the C2,3O gene product was confirmed by immunoblotting. We have mapped the 5' ends of the gene 32/xylE hybrid transcripts. In all of the Gram-negative bacteria, the proximal P2 promoter is the most efficient promoter in the cassette. In most of the strains a weaker and more distal promoter activity (Pl) was also detected. In both uninfected and phage-infected Escherichia coli cells, the transcript produced from this promoter is processed at a specific site upstream from the gene 32 start codon. The same processing occurred in all the bacterial species examined. The decay of the hybrid xylE transcript has been analyzed in E. coli and Erwinia, and in both strains this mRNA was among the most stable.

Escherichia coli and Pseudomonas putida RNA polymerases display identical contacts with promoters

Methylation protection experiments with four promoters (P1 and P2 of the pBR322 plasmid, lacUV5 and lambda P0) have shown that the RNA polymerases from Escherichia coli and Pseudomonas putida, while differing in the primary structure of the subunits involved in DNA binding, display identical patterns of DNA contacts. Nor do these enzymes differ in covalent cross-linking patterns with a partially apurinized promoter. We conclude that the two RNA polymerases have very similar structures of DNA binding centers. The evolutionary conservation of this structure may account for the fact that diverse RNA polymerases often recognize and efficiently use promoters of distant bacterial species.

Antigenic variability of bacterial RNA polymerases

Radioimmunoassay analysis of enteric and some other Gram-negative bacteria has shown that the antigenic structure of the RNA polymerase alpha subunit is more conserved than that of the beta and beta' subunits. Since anti-alpha antibodies do not affect RNA polymerase activity, the constraints which determine the low variability of the antigenic structure of the alpha subunit are not directly related to its functional role. The antigenic determinants of the alpha subunit located on the surface of the RNA polymerase molecule are more conserved than those involved in contacts with other subunits; an opposite tendency characterizes the beta subunit. The range of variability of the antigenic determinants buried inside the RNA polymerase molecule suggests that the subunits are attached to each other rather loosely. Immunological comparison of RNA polymerases provides a simple method for reconstructing bacterial genealogies. The genealogy of the bacteria examined is essentially in agreement with phylogenetic trees based on 16S and 5S rRNA sequence characterization. This argues against extensive interspecific transfer of genes coding for components of the transcription and translation apparatus.