The DNA sequence of argI from Escherichia coli K12.

The argI gene from E. coli K12 has been sequenced. It contains an open reading frame of 1002 bases which encodes a polypeptide of 334 amino acids. Three such polypeptides are required to form the functional catalytic trimer (c3) of ornithine transcarbamoylase (OTCase-1, EC 2.1.3.3). The molecular mass of the mature trimer deduced from the amino acid sequence is 114,465 daltons. An altered form of argI was produced when a 1.6 kilobase DdeI fragment was subcloned into the HincII site of plasmid pUC8 extending the open reading frame an additional 20 nucleotides. It has been previously reported that the amino-terminal region of the respective polypeptides of argI, argF, and pyrB of E. coli possessed significant homology. In contrast, the homologous promoter/operator regions of argI and argF did not appear to share any homologies with pyrB. However, a closer scrutiny of the nucleotide sequence immediately preceding the pyrBI attenuator revealed a remarkable similarity to the argI and argF control region.