A GENE ENCODING A PUTATIVE MEMBRANE-PROTEIN HOMOLOGOUS TO THE MAJOR FACILITATOR SUPERFAMILY OF TRANSPORTERS MAPS UPSTREAM OF THE BETA-GLYCOSIDASE GENE IN THE ARCHAEON SULFOLOBUS-SOLFATARICUS

We have identified a gene encoding a putative membrane protein homolog ous to the major facilitator superfamily, mapping upstream of the lacS gene in Sulfolobus solfataricus. Permeases from this family mediate s econdary transport and are widely distributed among eubacteria and euk aryotes; the finding of an archaeal member suggests that this mechanis m of transport evolved before the divergence of the three living domai ns. We also report a transcriptional mapping of the gene cluster.