A 54-kDa fragment of the Poly(A)-specific ribonuclease is an oligomeric, processive, and cap-interacting Poly(A)-specific 3' exonuclease.

• We have previously identified a HeLa cell 3' exonuclease specific for degrading poly(A) tails ofmRNAs, Here we report on the purification and identification of a calf thymus 54-kDa polypeptide associated witha similar 3' exonuclease activity. The 54-kDa polypeptide was shown to be a fragment of the poly(A)-specificribonuclease 74-kDa polypeptide. The native molecular mass of the nuclease activity was estimated to be 180-220 kDa, Protein/protein cross-linking revealed an oligomeric structure, most likely consisting of three subunits.The purified nuclease activity released 5'-AMP as the reaction product and degraded poly(A) in a highlyprocessive fashion. The activity required monovalent cations and was dependent on divalent metal ions. TheRNA substrate requirement was investigated, and it was found that the nuclease was highly poly(A)-specific and that only 3' end-located poly(A) was degraded by the activity. RNA substrates capped with m(7)G(5')ppp(5')G were more efficiently degraded than noncapped RNA substrates. Addition of free m7G(5')ppp(5')G cap analogue inhibited poly(A) degradation in vitro, suggesting a functional link between the RNA 5' end cap structure andpoly(A) degradation at the 3' end of the RNA.

Nyckelord

Adenosine Monophosphate/metabolism

Animals

Cattle

Chromatography; Affinity/methods

Exoribonucleases/isolation & purification/*metabolism

Movement

Peptide Fragments/metabolism

Protein Binding

Protein Structure; Quaternary

RNA Caps/*metabolism

RNA Processing; Post-Transcriptional

Substrate Specificity

Thymus Gland/*enzymology

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