The 7-nt conserved motif, histone 3′ stem-loop, and histone downstream element (HDE) that base-pairs with U7 snRNA are schematized. Stimulation of cleavage is proposed to occur when SF3b130 and SF3b49 mediate contact between U2 snRNP and CPSF, which contains the putative endonuclease for U7-snRNP-dependent cleavage, CPSF73 (Dominski et al., 2005; Kolev and Steitz, 2005). In contrast to the stimulation of CPA, where U2 snRNA-branchpoint interactions are critical (Kyburz et al., 2006), here the stimulatory RNA element is recognized by protein (but can be substituted by RNA-RNA) interactions.