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Cleavage and polyadenylation factor CPF specifically interacts with the pre‐mRNA 3′ processing signal AAUAAA.

Cleavage and polyadenylation factor (CPF) is required for the cleavage as well as for the subsequent polyadenylation reaction during 3′ processing of messenger RNA precursors. Here, we have investigated the interaction of CPF and poly(A) polymerase with short RNA substrates. CPF activates poly(A) polymerase to elongate RNA primers carrying the canonical hexamer recognition signal AAUAAA. CPF specifically binds to such RNA as shown by gel mobility shift assays and competition experiments. Upon binding of CPF, two polypeptides of 35 kDa and 160 kDa can be covalently crosslinked to the RNA by irradiation with UV light. These polypeptides may correspond to the smallest and the largest subunit contained in purified CPF fractions. In addition, chemical modification‐exclusion experiments demonstrate that CPF interacts directly with the AAUAAA recognition signal in the RNA. The entire hexamer signal is involved in binding of CPF since modification of any of its bases interferes with complex formation.