PNPase autocontrols its expression by degrading a double-stranded structure in the pnp mRNA leader.
Polynucleotide phosphorylase synthesis is autocontrolled at a post-transcriptional level in an RNase III-dependent mechanism. RNase III cleaves a long stem-loop in the pnp leader, which triggers pnp mRNA instability, resulting in a decrease in the synthesis of polynucleotide phosphorylase. The staggered cleavage by RNase III removes the upper part of the stem-loop structure, creating a duplex with a short 3' extension. Mutations or high temperatures, which destabilize the cleaved stem-loop, decrease expression of pnp, while mutations that stabilize the stem increase expression. We propose that the dangling 3' end of the duplex created by RNase III constitutes a target for polynucleotide phosphorylase, which binds to and degrades the upstream half of this duplex, hence inducing pnp mRNA instability. Consistent with this interpretation, a pnp mRNA starting at the downstream RNase III processing site exhibits a very low level of expression, regardless of the presence of polynucleotide phosphorylase. Moreover, using an in vitro synthesized pnp leader transcript, it is shown that polynucleotide phosphorylase is able to digest the duplex formed after RNase III cleavage.
Jarrige
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UPR9073 du CNRS, Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, 75005 Paris, France.
Mathy
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Portier
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D020121:5' Untranslated Regions; D001483:Base Sequence; D001665:Binding Sites; D004722:Endoribonucleases / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology; D029968:Escherichia coli Proteins; D015971:Gene Expression Regulation, Enzymologic; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D010957:Plasmids / Q000378:metabolism; D011062:Polynucleotide Adenylyltransferase / Q000378:metabolism; D011117:Polyribonucleotide Nucleotidyltransferase / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D043244:Ribonuclease III; D012260:Ribonucleases / Q000378:metabolism; D013696:Temperature; D013997:Time Factors
D020121:5' Untranslated Regions; D029968:Escherichia coli Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D011062:Polynucleotide Adenylyltransferase; D011117:Polyribonucleotide Nucleotidyltransferase; D004722:Endoribonucleases; D012260:Ribonucleases; D043244:Ribonuclease III; C468366:ribonuclease III, E coli