Transport of uridine in Escherichia coli B and A showdomycin-resistant mutant

The mechanism of uridine transport in Escherichia coli B cells was studied using experimental approaches designed to limit possible ambiguities in interpretation of data obtained previously. For this purpose, the transport of 2-¹⁴C]uridine and U-¹⁴C]uridine was determined in E. coli B and an E. coli B mutant which is resistant to the inhibitory effects of the nucleoside antibiotic, showdomycin.The majorty of the uridine transported as the intact nucleoside is cleaved to uracil and ribose l-phosphate. The uracil, in large part, is excreted, while ribose l-phosphate is retained. In addition, uridine is also rapidly cleaved to uracil and ribose l-phosphate in the periplasmic space. The uracil moiety may enter the cell, whereas ribose l-phosphate is not transported. The showdomycin-resistant mutant transports the intact nucleoside inefficiently, or not at all, but retains its ability to convert uridine to uracil in the periplasmic space.