The genes encoding the two carboxyltransferase subunits of Escherichia coli Acetyl-CoA carboxylase

We report characterization of the component proteins and molecular cloning of the genes encoding the two subunits of the carboxyltransferase component of the Escherichia coli acetyl-CoA carboxylase. Peptide mapping of the purified enzyme component indicates that the carboxyltransferase component is a complex of two nonidentical subunits, a 35-kDa α subunit and a 33-kDa β subunit. The α subunit gene encodes a protein of 319 residues and is located immediately downstream of the polC gene (min 4.3 of the E. coli genetic map). The deduced amino acid composition, molecular mass, and amino acid sequence match those determined for the purified α subunit. Six sequenced internal peptides also match the deduced sequence. The amino-terminal sequence of the β subunit was found within a previously identified open reading frame of unknown function called dedB and usg (min 50 of the E. coli genetic map) which encodes a protein of 304 residues. Comparative peptide mapping also indicates that the dedB/usg gene encodes the β subunit. Moreover, the deduced molecular mass and amino acid composition of the dedB/usg-encoded protein closely match those determined for the β subunit. The deduced amino acid sequences of α and β subunits show marked sequence similarities to the COOH-terminal half and the NH₂-terminal halves, respectively, of the rat propionyl-CoA carboxylase, a biotin-dependent carboxylase that catalyzes a similar carboxyltransferase reaction reaction. Several conserved regions which may function as CoA-binding sites are noted.