Polynucleotide phosphorylase functions as both an exonuclease and a poly(A) polymerase in spinach chloroplasts.

ABSTRACT: The molecular mechanism of mRNA degradation in the chloroplast consists of sequential events including endonucleolytic cleavage, the addition of poly(A)-rich sequences to the endonucleolytic cleavage products, and exonucleolytic degradation by polynucleotide phosphorylase (PNPase). In Escherichia coli, polyadenylation is performed mainly by poly(A)-polymerase (PAP) I or by PNPase in its absence. While trying to purify the chloroplast PAP by following in vitro polyadenylation activity, it was found to copurify with PNPase and indeed could not be separated from it. Purified PNPase was able to polyadenylate RNA molecules with an activity similar to that of lysed chloroplasts. Both activities use ADP much more effectively than ATP and are inhibited by stem-loop structures. The activity of PNPa

SUBMITTER: Yehudai-Resheff S 

PROVIDER: S-EPMC87263 | biostudies-literature | 2001 Aug

REPOSITORIES: biostudies-literature