The 30-kD subunit of mammalian cleavage and polyadenylation specificity factor and its yeast homolog are RNA-binding zinc finger proteins.

  1. S M Barabino,
  2. W Hübner,
  3. A Jenny,
  4. L Minvielle-Sebastia, and
  5. W Keller
  1. Department of Cell Biology, Biozentrum, University of Basel, Switzerland.

Abstract

Cleavage and polyadenylation specificity factor (CPSF), a key component of the mammalian RNA 3'-end processing machinery, consists of four subunits of 160, 100, 73, and 30 kD. Here we report the isolation and characterization of a cDNA encoding the 30-kD polypeptide. Antibodies raised against this protein inhibit cleavage and polyadenylation and coimmunoprecipitate the other CPSF subunits. The protein sequence contains five C3H-zinc-finger repeats and a putative RNA-binding zinc knuckle motif at the carboxyl terminus. Consistent with this observation, the in vitro translated 30-kD protein binds RNA polymers with a distinct preference for poly(U). In addition, an essential S. cerevisiae gene, YTH1, was cloned which is 40% identical to CPSF 30K at the protein level. Extracts prepared from a conditional yth1 mutant have normal cleavage activity, but fail to polyadenylate the upstream cleavage product. Efficient polyadenylation activity can be restored by the addition of purified polyadenylation factor I (PF I). We demonstrate that Yth1p is a component of PF I that interacts in vivo and in vitro with Fip1p, a known PF I subunit.

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