We describe a bacterial RNA polymerase mutation, rif 501, which confers rifampicin resistance and thermosensitivity to E. coli K 12. The purified RNA polymerase enzyme from rif 501 bacteria shows increased heatsensitivity in vitro at 51 degrees C. However, in vivo, at 42 degrees C the non-permissive temperature, mutant bacteria continue to grow and to synthesize RNA for 90 min. On a lawn of the mutant bacteria, at 40-41 degrees C, phage lambda forms clear plaques (LycA phenotype); this is probably due to an enhancement of cro function; we surmise that at 42 degrees C the transcription originating from the pR (but not from the pL) promoter on the lamdba genome becomes N-independent and less sensitive to the absence of the cro product. We discuss the possibility that both the N and cro proteins of phage lambda interact directly with the bacterial RNA polymerase. These observations indicate that the loss of viability of the rif 501 mutant at the restrictive temperature is not a consequence of an immediate inactivation of RNA polymerase; rather we feel it is due to a modification of the activity of RNA polymerase, leading to a disruption of the cellular regulation.
A N-lambda bacteriophage transducing the structural genes for Escherichia coli K-12 carbamoylphosphate synthase (glutamine) (CPSase; EC 2.7.2.9) has been isolated and analyzed both genetically and physically. The whole int-N region is substituted for a short chromosomal segment corresponding almost exactly to the car locus. The study of CPSase, ornithine carbamoyltransferase, and aspartate carbamoyltransferase regulation in carriers of lambdadcar confirms the previously reported participation of the argR gene product in the control of CPSase synthesis and points to the existence of a regulatory molecule involved in the control of both CPSase and aspartate carbamoyltransferase synthesis. The general usefulness of using N- lambda transducing bacteriophages for the recovery of large amounts of gene products is discussed.
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