[Is it reality that the endonuclease that cleaves pre-mRNA on polyadenylation has not been discovered?]

Specific cleavage of transcript by a complex of multisubunit proteins is the first stage of polyadenylation of eukaryotic pre-mRNAs. The main participant of this reaction--endonuclease--is not discovered yet. However it is known that proteins CPSF-30 (mammalian) and Yth 1p (yeast) are homologues of the drosofila protein clipper (CLP), which displays endoribonucleolytic activity. In the N-terminal region all three proteins contain five copies of CCCH zinc finger motif that are associated with nucleolytic activity in the case of CLP. Literature data on the three above-mentioned proteins has been analysed. The results of these works do not contradict the hypothesis that exactly CPSF-30 and its homologues are the actual nucleases that cleave pre-mRNA in the process of polyadenylation.