Interaction of poly(A) polymerase with the 25-kDa subunit of cleavage factor I

Mammalian poly(A) polymerase (PAP), a key enzyme in the pre-mRNA 3'-end pro cessing reaction, carries the catalytic domain in the N-terminal region, an RNA binding domain, two nuclear localization signals, and a serine/threoni ne-rich regulatory domain in the C-terminal region. Using LexA-based yeast two-hybrid screening, we identified a cDNA encoding the 25-kDa subunit of c leavage factor I (CFI-25) as a protein that interacts with the C-terminal r egion of mouse PAP. The glutathione S-transferase pull-down assay and the i mmunoprecipitation experiment revealed that PAP directly interacts with CFI -25 and that the C-terminal 69 residues of PAP and the N-terminal 60 residu es of CFI-25 are sufficient for the interaction between CFI-25 and PAP. Sin ce CFI is known to function in the assembly of the pre-mRNA 3'-processing c omplex, this interaction may play an important role in the assembly of the processing complex and/or in the regulation of PAP activity within the comp lex. (C) 2001 Elsevier Science.