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Phenotype of htgA (mbiA), a recently evolved orphan gene of Escherichia coli and Shigella, completely overlapping in antisense to yaaW

FEMS Microbiology Letters
September 24, 2013

Overlapping embedded genes, such as htgA/yaaW, are assumed to be rare in prokaryotes. In Escherichia coli O157:H7, gfp fusions of both promoter regions revealed activity and transcription start sites could be determined for both genes. Both htgA and yaaW were inactivated strand specifically by introducing a stop codon. Both mutants exhibited differential phenotypes in biofilm formation and metabolite levels in a nontargeted analysis, suggesting that both are functional despite YaaW but not HtgA could be expressed. While yaaW is distributed all over the Gammaproteobacteria, an overlapping htgA‐like sequence is restricted to the Escherichia‐Klebsiella clade. Full‐length htgA is only present in Escherichia and Shigella, and htgA showed evidence for purifying selection. Thus, htgA is an interesting case of a lineage‐specific, nonessential and young orphan gene.