Activating cyclin for the cyclin-associated kinase CDK10. Associates with CDK10 to promote its kinase activity. Interacts with SALL1. The disease is caused by variants affecting the gene represented in this entry. Silencing with siRNAs phenocopies CDK10 silencing in increasing c-Raf and in conferring tamoxifen resistance to breast cancer cells. Belongs to the cyclin family. Cyclin-like FAM58 subfamily.