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

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.