THE STREPTOMYCES ATP-BINDING COMPONENT MSIK ASSISTS IN CELLOBIOSE ANDMALTOSE TRANSPORT

Streptomyces reticuli harbors an msiK gene which encodes a protein wit h an amino acid identity of 90% to a corresponding protein previously identified in Streptomyces lividans, Immunological studies revealed th at S. lividans and S. reticuli synthesize their highest levels of MsiK during growth with cellobiose, but not with glucose, Moreover, modera te amounts of MsiK are produced by both species in the course of growt h,vith maltose, melibiose, and xylose and by S. lividans in the presen ce of xylobiose and raffinose. In contrast, a recently identified cell obiose-binding protein and its distantly related homolog were only fou nd if S. reticuli or S. lividans, respectively, was cultivated with ce llobiose. Uptake of cellobiose and maltose was tested and ascertained for S. reticuli and S. lividans, but not for an msiK S. lividans mutan t. However, transformants of this mutant carrying the S. reticuli or S . lividans msiK gene on a multicopy plasmid had regained the ability t o transport both sugars, The data show that MsiK assists two ABC trans port systems.