Nucleotide Sequence of the Glycerol-3-phosphate Dehydrogenase Gene of Escherichia coli and Regulation by the cAMP-CRP Complex

Abstract

The glpD gene, which codes for glycerol-3-phosphate dehydrogenase, was cloned from the genomic library of Escherichia coli. The nucleotide sequence of the glpD gene contained a single open reading frame of 503 amino acid residues. Two new open reading frames, ORFX1 and ORFX2, were located downstream from the glpD gene. The two open reading frames were separated from the glpD gene by repetitive extragenic palindromic units. The putative ORFX1 protein was composed of 97 amino acid residues. The ORFX2 encoded a truncated protein. Computer-assisted analysis of the nucleotide sequence showed that homology in amino acid sequences between ORFX2 protein and rabbit glgP, human glgP, potato glgP, and E. coli malP was 50.6, 51.3, 40.5, and 46.8%, respectively. The operon of glycogen synthesis was closely linked to the glpD gene on the E. coli chromosome. These results suggested that ORFX2 was a truncated protein of the glycogen phosphorylase gene.
The deduced primary structure of the glpD protein contains a putative flavin binding site at the N-terminus. Expression of the subcloned glpD gene was positively regulated by the cAMP-CRP complex. The enzyme activity of glycerol-3-phosphate dehydrogenase increased after introduction of a multicopy of the glpD gene.