Inhibition of nucleoside-binding sites by nucleoside analogues in Escherichia coli.

SUMMARY Nucleoside analogues modified in heteroeyclic bases or sugar moieties were screened for their ability of counteracting the bacteriostatic effect of showdomycin in E. colio Pyrimidine ribonucleosides or 2-deoxyribonucleosides substituted at the position 5 wijh halogen^atom, methyl or hydroxyl group, 2-fluoro-, 2-chloro-2-deoxyuridme and its 5-methyl homologue, N^-dimethylcytidine and N*-acetylcytidine, isoeytidine, l-Tp-D-ribofuranosyl)-4-aminopyrimidine-6-one, isoguanosine, purine riboside, the N°-and 8-substituted derivatives of adenosine, were a l l effective. With the exception of 5-hydroxyuridine, all these compounds were non-toxic in E. c o l i. The same group of compounds was shown to inhibit competitively the phosphorolysis of 2-deoxythymidine in whole c e l l s , being inactive in cell-free extracts. The analogues apparently compete for a common nucleoside-binding site at the surface of the c e l l s. Showdomycin i t s e l f does not cause any irreversible inactivation of nucleoside-binding s i t e s. INTRODUCTION The b a c t e r i o s t a t i c a c t i v i t y of the a n t i b i o t i c showdomycin i s dependent on i t s uptake mediated by n u c l e o s i d e-t r a n s p o r t i n g system. Mutants d e f i c i e n t i n a component of t h i s system become completely resistant to the drug. Alternatively, the antibiotic may be detozicated by a number of nucleosides which enter the c e l l s by the same route and presumably compete for common nucleoside-binding sites or permease; this group of antagonists includes pyrimidine as well as purine ribonucleosides and 2*-deoxyribonueleosidee with the notable exception of guanosine and deoxyguanosine • Showdomycin may thus become very useful in a search for compounds specifically interacting with bacterial nucleoside-transporting systems. Examining a large number of aucleoside analogues we discovered many antagonists of showdomycin, most of them apparently representing specific in