, Volume 137, Issue 4, pp 327-335

Multiple regulation of nucleoside catabolizing enzymes: Regulation of thedeo operon by thecytR anddeoR gene products

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Summary

The protein and repressor nature of two regulatory gene products inE. coli has been demonstrated, employing mutants with either amber or thermosensitive mutations. The regulatory genes are thecytR and thedeoR genes, both of which contribute to the regulation of the synthesis of nucleoside catabolizing enzymes.

Enzyme levels in strains with concurrent mutations in both regulatory genes are considerably higher than the sum of the levels in strains with acytR or adeo R mutation alone, indicating a certain co-operativity between the two repressor proteins.

The glucose repression of enzyme levels observed in the double regulatory mutant is similar to that found in acytR mutant, and much more pronounced than the glucose effect in adeo R mutant.

A model of the promoter-operator region in thedeo operon is proposed.

Abbreviations and Symbols. Genes coding for: cytidine deaminase,cdd; uridine phosphorylase,udp; thymidine phosphorylase,ipp; purine nucleoside phosphorylase,pup; uridine kinase (=cytidine kinase),udk;Cyt R = regulatory gene forcdd, udp, dra, tpp, drm, andpup. Deo R regulatory gene fordra, tpp, drm, andpup. This regulatory gene is believed to be identical to thenuc R gene described by Ahmad and Pritchard (1971). We have chosen the namedeo R for the gene, since the gene cluster controlled by this regulatory gene was originally designated thedeo operon by Lomax and Greenberg (1968). The namedeo R is also in agreement with the nomenclature used by Blank and Hoffee (1972) for the corresponding gene inSalmoeeella typhimurium. cAMP: cyclic adenosine 3:5′-monophosphate. CRP, cyclic AMP receptor protein. dRib5P: deoxyribose 5-phosphate
Enzymes. Purine nucleoside phosphorylase or purine nucleoside: orthophosphate (deoxy) ribosyltransferase (EC 2.4.2.1); thymidine phosphorylase or thymidine: orthophosphate deoxyribosyltransferase (EC 2.4.2.4); uridine phosphorylase or uridine: orthophosphate ribosyltransferase (EC 2.4.2.3); cytidine deaminase or (deoxy)cytidine aminohydrolase (EC 3.5.4.5); deoxyriboaldolase or 2-deoxy-D-ribose-5-phosphate; acetaldehydelyase (EC 4.1.2.4); phosphodeoxyribomutase
Communicated by E. Bautz