Molecular cloning, nucleotide sequence, and expression of shl, a new gene in the 2-minute region of the genetic map of Escherichia coli.

Cells of Escherichia coli that harbor supH (an allele of the wild-type gene serU) are sensitive to UV irradiation and temperature and appear to have an impaired cell division control mechanism. We found that a gene located at the 2-min region, designated shl, inhibited the growth of supH-harboring cells when carried by a high-copy-number plasmid, whereas the same plasmid had no visible effect when present in parental cells. The amino acid sequence predicted from the nucleotide sequence of the shl gene indicated a similarity to the GalR and LacI repressor proteins, suggesting it is a transcription regulator. The sequence between the promoter and the structural genes revealed the presence of a short open reading frame of 28 amino acid residues followed by a segment of 81 base pairs. These structural features suggest that a transcription antitermination mechanism may be involved in the regulation of expression of the shl gene. The possibility that shl is a regulator of serU is discussed.