Regulatory component of the cyclin-L-CDK11 complex that regulates transcription and pre-mRNA splicing (PubMed:11980906, PubMed:18216018, PubMed:38059508). Inhibited by the CDK-specific inhibitor CDKN1A/p21 (PubMed:11980906). May be a candidate proto- oncogene in head and neck squamous cell carcinomas (HNSCC) (PubMed:12414649, PubMed:15700036). {ECO:0000269|PubMed:11980906, ECO:0000269|PubMed:12414649, ECO:0000269|PubMed:15700036, ECO:0000269|PubMed:18216018, ECO:0000269|PubMed:38059508}. This is the function of Ensembl gene identifier ENSG00000163660 (CCNL1, cyclin L1).