Transcriptional cofactor (PubMed:17933794). Required for controlling cell proliferation in the seam cells, a stem cell-like lineage, acting in concert with Runt-related transcription factor 1 rnt-1, perhaps by repressing expression of cyclin-dependent kinase inhibitor cki-1 (PubMed:17933794). Represses expression of rnt-1 (PubMed:18158917). Regulates male tail development (PubMed:17933794). May play a role in vulval and/or uterine morphogenesis (PubMed:17933794). Interacts with rnt-1; acts to increase the affinity and specificity of interaction of rnt-1 with DNA. Expressed throughout development from the late embryonic stage (PubMed:18158917). Expressed in all larval stages, in H0-2, V1-6, and T seam progeny, and in the uterine seam cells (utse) during late larval stage L4 in hermaphrodites (PubMed:17933794). Expressed in some body wall muscle cells and some pharyngeal neurons (PubMed:17933794). RNAi-mediated knockdown increases expression of Runt-related transcription factor rnt-1. Belongs to the CBF-beta family.