ACTIVE-TRANSPORT BY THE CSCB PERMEASE IN ESCHERICHIA-COLI K-12

The cscB gene encoding a putative sucrose permease from Escherichia co li EC3132 [Bockmann, J., Heuel, H. & Lengeler, J. W. (1992) Mol. Gen. Genet. 235, 22-32] was placed under control of the lacZ promoter/opera tor and overexpressed. Cells of E. coli K-12 expressing cscB gene prod uct from a high copy number plasmid accumulate sucrose against a conce ntration gradient with an apparent K-m of about 1 mM and a V-max of ap proximately 23 nmol/min/mg protein. In contrast, transport of lactose or melibiose is not observed. Epitope-tagging and immunological analys is reveal that concomitant with increased transport activity, a protei n with an apparent M(r) of 33-34 kDa appears in the cytoplasmic membra ne. The results provide direct support for the contention that the csc B gene encodes a sucrose permease and provide the basis for further mo lecular analysis. (C) 1995 Academic Press, Inc.