FIG. 2.

Assay of NXP transport by Tlc4 (A) and Tlc5 (B). The tlc4 and tlc5 genes were cloned into the pET-11a expression vector and introduced into the C41 strain of E. coli by electroporation. Cultures were grown, induced, and assayed for the transport of ATP, CTP, UTP, GTP, and GDP as described in Materials and Methods. All NXPs were added at a concentration of 1 mM (with 1 to 2 μCi/ml of the appropriate α-³²P-labeled nucleotide phosphate), and uptake reactions were initiated by the addition of cells. Symbols: ATP, open squares; CTP, filled squares; UTP, filled diamonds; GTP, open triangles; and GDP, filled triangles.