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Pseudomonas aeruginosa; Escherichia coli--Genetics; Genetic translation


Pseudomonas aeruginosa has two anthranilate synthase (AS) gene pairs. One AS enzyme participates in tryptophan synthesis; its genes are designated trpE and trpG The other AS enzyme, encoded by phnA and phnB, participates in the synthesis of pyocyanin, the characteristic phenazine pigment of the organism. The phenazine pathway genes phnA and phnB overlap by 23 base pairs, excluding the phnB Shine-Dalgarno region, with pbnA upstream from phnB. Our objective was to examine the cloned P. aeruginosa phnA and pbnB gene pair for translational coupling in Escherichia coli. The first 113 base pairs of phnB were fused with either LacZ or its a-peptide. By altering the reading frame in which ribosomes entered the phnA segment, the level of expression of the phnB-lacZ fusion protein was affected. Measurement of phnB-lacZ fusion mRNA and N-terminal sequencing of purified fusion proteins established that the observed differences in expression were indeed translational and not transcriptional. Our results suggest that translational coupling can occur within the 23 base pair overlap between phnA and phnB.

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