Figure 6. Possible routes of regulation by RBM7 in promoting splicing. Depicted is the 3' exon of the pre-mRNA selected for splicing and portion of its 5' intron with adjacent sequence bound by U2 snRNA at the branch point sequence during spliceosome assembly. The pre-mRNA is linearized and SF3a within U2 snRNP is simplified for illustration purposes. The nomenclature of SAPs is followed. RBM7 may either 1) substitute for SAP49 function in cells lacking SAP49, 2) modulate SAP49 and SAP145 interaction via its own interaction with SAP145, or 3) recruit SAP145 to near the branch site via SRp20 bound to an exon splicing enhancer (ESE) in ESE-dependent splicing. Note that the sphere of influence of SR extends throughout constitutive splicing and may recruit RBM7 via SRp20. 3'ss indicates the 3' splice site; A, branch point adenosine; x, protein-RNA interaction; and •, protein-protein interaction. Based on Will and Luhrmann (1997).