DNA sequence of the genescrAencoding the sucrose transport protein EnzymellScrof the phosphotransferase system from enteric bacteria: homology of the EnzymellScrand EnzymellBglproteins

The nucleotide sequence of the structural gene, scrA, which codes for sucrose-specific EnzymellScr (EIIScr ) of the phosphoenolpyruvate-dependent carbohydrate: phosphotransferase system (PTS), was determined. EllScr requires an Enzymelll, the product of the gene crr, for full activity. The gene scrA is preceded immediately by a classical Shine-Dalgarno sequence (AAGAGGGTA). It contains 1368 nucleotides with an increased GC-content (58%) corresponding to a polypeptide of 455 amino acid residues (Mr 47 500). The protein has the hydropathic profile (average hydropathy +0.82) of an integral membrane protein lacking extended α-helical structures and a signal peptide. Comparison with the sequence of the β-glucoside-specific Enzymell (EllBgl , 625 amino acids, Mr 66480; Bramley and Kornberg, 1987a; Schnetz et al., 1987) revealed strong homologies between EllScr and the first 458 residues of EllBgl . The 162 carboxyterminal residues of EllBgl , however, showed a high homology with the sequence of Enzymelll (Nelson et al., 1984), a homology also described recently by Bramley and Kornberg (1987b). The evolutionary and functional significance of the similarities with four other Enzymesll is discussed.