Structure and organization of hip, an operon that affects lethality due to inhibition of peptidoglycan or DNA synthesis

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Abstract
High-frequency persistence to the lethal effects of inhibition of either DNA or peptidoglycan synthesis, the Hip phenotype, results from mutations at the hip locus of Escherichia coli K-12. The nucleotide sequence of DNA fragments which complement these mutations revealed an operon consisting of a possible regulatory region, including sequences with modest homology to an E. coli promoter, and two open reading frames which are translated both in vitro and in vivo. The stop codon of a 264-bp open reading frame, hipB, and the start codon of a 1,320-bp open reading frame, hipA, share an adenine residue. Assays of promoter strength, the location of the probable promoter with respect to the start of transcription, and codon usage all indicate that hipB and hipA are weakly expressed genes. The activity of the promoter is impaired by an adjacent downstream sequence which includes the coding region of hipB. The impairment is partially relieved by insertion of a premature translation termination signal within the coding region of hipB, suggesting involvement of the HipB protein in the regulation of this promoter. The arrangement of hipB and hipA within the operon and the toxicity of hipA for strains defective in or lacking hipB suggest an important interaction between the products of these genes.