The complementary C-strand at telomeres is synthesized by the polymerase alpha:primase complex using conventional RNA priming (Nakamura et al. 2005, Dai et al. 2010). This process is regulated by the CST complex (Dai et al. 2010, Feng et al. 2017, Feng et al. 2018) and CDK1 (Dai et al. 2010, Dai et al. 2012).