The polyadenylation complex – Endonucleases

July 31, 2008

Messenger RNA 3’ end formation involves an RNA processing step.  It is thus natural to assume that the polyadenylation complex (as illustrated here) includes at least one subunit that is an endonuclease (an enzyme that cuts the RNA within the polynucleotide chain, as opposed to at the 5′ or 3′ ends).  Indeed, the complex does include such a nuclease.  However, just as there seem to be more RNA binding proteins than known cis element, there may be a multiplicity of endonucleases in the complex.  Specifically, at least two CPSF subunits (CPSF73 and CPSF30) have been shown to possess endonucleolytic activity in vitro (1-4).  The research community would probably consider that CPSF73 is the most probable candidate for THE processing endonuclease, but the possibility that CPSF30 serves this role, along with or instead of CPSF73, cannot be ruled out.  (Except perhaps in yeast, whose CPSF30 counterpart, Yth1, apparently lacks the nuclease activity seen in other eukaryotic homologs [5].)

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