In bacteria there are a number of families of transport proteins that mediate the intake of a variety of sugars with the concomitant uptake of hydrogen ions (proton symporters) [1]. One of these families is composed [2] of the following proteins:

• Escherichia coli and Klebsiella pneumoniae lactose permease (gene lacY) which are responsible for the transport of β-galactosides into the cell.
• Escherichia coli plasmid pRsd2 raffinose permease (gene rafB).
• Escherichia coli sucrose permease (gene cscB).

These integral membrane proteins are predicted to comprise twelve membrane spanning domains. As signature patterns we selected two conserved regions that both correspond to cytoplasmic loops: between the second and third transmembrane regions for the first pattern and between the eight and ninth for the second pattern.