Structure and expression of cysX, the second gene in the Escherichia coli K-12 cysE locus

Protein products of the cysE region at 81 min on the chromosome of Escherichia coli K-12 (1) were analyzed by the maxicell method. Two kinds of polypeptides of molecular weight 33 K and 16 K were the products. The open reading frame (ORF) of the 33 K polypeptide consisted of 273 amino acids (Mr = 29,261). On the other hand, the 16 K ORF was overlapped by the opposite 33 K ORF and specified an extremely basic protein of 130 amino acids (Mr = 15,233). The gene coding for the 16 K polypeptide was named cysX. The expression of cysE and cysX in vivo was confirmed further by constructions of the cysE'-'lacZ and cysX'-'lacZ hybrid genes.