DNA-binding protein involved in cell cycle control. May act as a transcription activator. Plays role in pre-mRNA splicing as core component of precatalytic, catalytic and postcatalytic spliceosomal complexes. Component of the PRP19-CDC5L complex that forms an integral part of the spliceosome and is required for activating pre-mRNA splicing. The PRP19-CDC5L complex may also play a role in the response to DNA damage (DDR). Homodimer. Interacts with DAPK3 (By similarity). Component of the precatalytic, catalytic and postcatalytic spliceosome complexes (By similarity). Part of a spliceosomal 'core' complex consisting of CDC5L, PLRG1, SPF27, CCAP1, CCAP3 and CCAP6. Interacts with PLRG1, Lodestar/TTF2, and NIPP1/PPP1R8. Component of the PRP19-CDC5L splicing complex composed of a core complex comprising a homotetramer of PRPF19, CDC5L, PLRG1 and BCAS2, and at least three less stably associated proteins CTNNBL1, CWC15 and HSPA8. Interacts (via its C-terminus) directly in the complex with PRPF19 and BCAS2. Interacts (via its C-terminus) directly with PRGL1 (via its WD40 repeat domain); the interaction is required for mRNA splicing but not for spliceosome assembly. Also interacts with CTNNBL1. Interacts with PRPF19 (via N-terminus) (By similarity). Interacts with USB1 (By similarity). May shuttle between cytoplasm and nucleus. Phosphorylated on serine and threonine residues. Phosphorylation on Thr-411 and Thr-438 is required for CDC5L-mediated mRNA splicing. Has no effect on subcellular location nor on homodimerization. Phosphorylated in vitro by CDK2. Phosphorylation enhances interaction with PPP1R8. Belongs to the CEF1 family.