Abstract
Polynucleotide phosphorylase (PNPase) is a 3′–5′-exoribnuclease that is found in most bacteria and in some eukaryotic organelles. The enzyme plays a key role in RNA decay in these systems. PNPase structure and function have been studied extensively in Escherichia coli, but there are several important aspects of PNPase function in Streptomyces that differ from what is observed in E. coli and other bacterial genera. This review highlights several of those differences: (1) the organization and expression of the PNPase gene in Streptomyces; (2) the possible function of PNPase as an RNA 3′-polyribonucleotide polymerase in Streptomyces; (3) the function of PNPase as both an exoribonuclease and as an RNA 3′-polyribonucleotide polymerase in Streptomyces; (4) the function of (p)ppGpp as a PNPase effector in Streptomyces. The review concludes with a consideration of a number of unanswered questions regarding the function of Streptomyces PNPase, which can be examined experimentally.
Highlights
PNPase distinguish it from its counterparts in other bacteria
One substrate, designated 5601, possessed a single stranded 3 -tail, 33 bases in length, while the other substrate, 5650, terminated at the base of the intergenic hairpin, and did not have a single stranded tail [47]. The phosphorolysis of these two substrates was studied in the absence and presence of a mixture of all four nucleoside diphosphates (NDPs) with the interesting result, predicted by our hypothesis, that the NDPs, normally the substrates for the polymerizing activity of PNPase, did stimulate RNA degradation by phosphorolysis
NDPs had no effect on the phosphorolysis of the 5601 substrate, possessing the single stranded tail
Summary
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