Specifically required for generation of multiciliated cells, possibly by promoting a cell cycle state compatible with centriole amplification and maturation. Acts downstream of MCIDAS to promote mother centriole amplification and maturation in preparation for apical docking. Localizes to the apical part of cytoplasm. Present in respiratory cells (at protein level). Maximum levels during G(1) phase. Levels decrease through S and G(2) phases. The disease is caused by variants affecting the gene represented in this entry. Marked reduction of cilia in multiciliate cells due to defective mother centriole generation and placement. Remaining cilia correctly express axonemal motor proteins, are motile and do not show beating defects. Defects are probably caused by a strong reduction in the number of multiple motile cilia covering the cell surface in respiratory epithelial cells (PubMed:24747639). Belongs to the cyclin family. Was originally thought to have uracil-DNA glycosylase (UDG) activity and wrongly named UNG2 and UDG2 (PubMed:2001396). It was later shown that it is a member of the cyclin family (PubMed:8419333). UNG2 corresponds to the isoform 2 of UNG gene. Sequencing errors. Sequencing errors.