SF3 is a U2 snRNP-associated protein complex essential for spliceosome assembly and splicing catalysis of the major spliceosome. SF3 contains the Spliceosome-Associated Proteins, SAP 49, 130, 145, and 155. SAP155/Sf3b1 is an essential subunit of the U2 snRNP for mRNA splicing and has also been identified in the minor (U12-dependent) spliceosome. SAP155 interacts with the mammalian PcG (Polycomb group) proteins, Mel18 and Ring1B by the yeast two-hybrid system. SAP155 contains numerous Cdk consensus phosphorylation sites in its N terminus and is phosphorylated prior to catalytic step II of the splicing pathway. SAP155 serves as a substrate for cyclin E-cdk2 in vitro, suggesting that pre-mRNA splicing may be linked to the cell cycle machinery in mammalian cells.Synonyms: Pre-mRNA-splicing factor SF3b 155 kDa subunit, SAP 155, SAP-155, SF3b155, Spliceosome-associated protein 155, Splicing factor 3B subunit 1