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 (PubMed:11991638, PubMed:20176811, PubMed:28502770, PubMed:28076346, PubMed:29361316, PubMed:29360106, PubMed:29301961, PubMed:30728453, PubMed:30705154). 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) (PubMed:20176811). Homodimer. Interacts with DAPK3 (By similarity). Component of the precatalytic, catalytic and postcatalytic spliceosome complexes (PubMed:11991638, PubMed:28502770, PubMed:28076346, PubMed:29361316, PubMed:29360106, PubMed:29301961, PubMed:30728453, PubMed:30705154). 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 (PubMed:23022480). May shuttle between cytoplasm and nucleus. Ubiquitously expressed in both fetal and adult tissues. 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. A chromosomal aberration involving CDC5L is found in multicystic renal dysplasia. Translocation t(6;19)(p21;q13.1) with USF2. Belongs to the CEF1 family. Extended N-terminus.