The glycerol facilitator is one of the few known examples of bacterial solute transport proteins that catalyse facilitated diffusion across the cytoplasmic membrane. A second protein, glycerol kinase, is involved in entry of external glycerol into cellular metabolism by trapping glycerol in the cytoplasm as -glycerol 3-phosphate. Evidence is presented that glycerol transport in is mediated by a similar transport system. The genes encoding the glycerol facilitator, and glycerol kinase, were isolated on a 4.5 kb fragment from a chromosomal mini-library by functional complementation of an mutant after establishing a map of the chromosomal region with the help of a PCR-amplified segment. The nucleotide sequence revealed that is the promoter-proximal gene of the operon. The glycerol facilitator and glycerol kinase were identified in a T7 expression system as proteins with apparent molecular masses of 25 and 56 kDa, respectively. The identities of the glycerol facilitator and glycerol kinase amino acid sequences with their counterparts from were 70 and 81%, respectively; this similarity extended to two homologues in the genome sequence of A chromosomal δ mutant was isolated by gene replacement. This mutant no longer transported glycerol and could no longer utilize it as sole carbon and energy source. Two ORFs, and encoding a putative regulatory protein and a carbohydrate kinase of unknown function, were located upstream of the operon.


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