NUCLEOTIDE-SEQUENCE AND 3'-END DELETION STUDIES INDICATE THAT THE K-UPTAKE PROTEIN KUP FROM ESCHERICHIA-COLI IS COMPOSED OF A HYDROPHOBIC CORE LINKED TO A LARGE AND PARTIALLY ESSENTIAL HYDROPHILIC-C TERMINUS()

The kup (formerly trkD) gene from Escherichia coli encodes a minor K+- uptake system. The gene is located just upstream of the rbsDACBK opero n at 84.5 min on the chromosome and is transcribed clockwise. kup code s for a 69-kDa protein, which may be composed of two domains. The firs t 440 amino acid residues appear to form an integral membrane protein that might traverse the cell membrane 12 times. The C-terminal 182 ami no acid residues are predicted to form a hydrophilic domain located at the cytoplasmic side of the membrane. Deletion studies from the 3' en d of kup showed that removal of almost the complete hydrophilic domain of the protein reduced, but did not abolish, K+-uptake activity.