CCNA2 binds to TICRR (also known as treslin or C15ORF42) in G2 (Pagliuca et al. 2011) and the CCNA2:CDK1 complex phosphorylates TICRR on CDK consensus sites S441, S838, S923, and T1260 (Pagliuca et al. 2011). The CCNA1:CDK1 complex is annotated as a candidate TICRR kinase. TICRR has previously been reported to be phosphorylated by the CCNA:CDK2 complex in vitro (Moritani and Ishimi 2013). TICRR is involved in the initiation of DNA replication (Kumagai et al. 2010). CDKs, primarily CDK2 (Kumagai et al. 2011, Sansam et al. 2015), but possibly also CDK1 (Sansam et al. 2015), regulate the length of S phase through TICRR phosphorylation (Kumagai et al. 2011, Sansam et al. 2015). In Drosophila, it was shown that CDK1 is needed for the replication of satellite sequences which occurs late during S phase, or at S/G2 boundary (Farrell et al. 2012).