The sequence of the malG gene from Salmonella typhimurium and its functional implications

The nucleotide sequence of the malG gene which is essential for maltose transport was determined in Salmonella typhimurium and compared to homologous genes from Escherichia coli and Enterobacter aerogenes. malG genes from S. typhimurium and E. aerogenes were expressed and their products were active in E. coli. The primary structure of the three MalG proteins was highly conserved. Changes were mainly clustered in a relatively large hydrophilic region of the protein (residues 40 to 75). In contrast, other hydrophilic segments were more conserved, and most remaining changes occurred in the hydrophobic putative transmembrane segments. This suggests that hydrophilic loops in this inner membrane protein may be functionally constrained. These results prove new insights into the functional sites in MalG.