Small, non-coding Y RNAs are abundant vertebrate RNAs. All four Y RNAs have an essential role in DNA replication and display functional redundancy. As Y RNAs are enriched in human solid tumours, understanding their molecular mechanism during replication and cell proliferation is of high importance. In this issue (p. 1239) Torsten Krude and Eyemen Kheir investigate the expression levels and dynamic association between Y RNAs and chromatin during the cell cycle of cancer and non-cancer cell lines. Although the authors find no differences between cancer and control cell lines, they report that Y RNAs are higher expressed in proliferating cells than in quiescent ones. Y RNAs associate with euchromatin and chromatin-bound RNA levels peak in S phase compared with other cell cycle stages. Furthermore, Krude and Kheir show that Y RNAs associate with early-replicating euchromatin in G1 phase are transiently displaced from active DNA replication foci in S phase and associate again with replicated euchromatin during later stages of S phase. Specifically, Y1 RNA is found to bind euchromatin with similar dynamics and at the same location as the origin recognition complex (ORC). Therefore, the dynamics of Y RNAs closely follow those of ORC, rather than those of subsequently assembled licensing factors. These data suggest that Y RNAs act in a common functional pathway with ORC to initiate DNA replication, and that they do not behave like licensing factors because they are found on replicated chromatin during late S phase.
