RT Journal Article SR Electronic T1 Punctuated evolution and transitional hybrid network in an ancestral cell cycle of fungi JF bioRxiv FD Cold Spring Harbor Laboratory SP 038372 DO 10.1101/038372 A1 Edgar M. Medina A1 Jonathan J. Turner A1 Jan M. Skotheim A1 Nicolas E. Buchler YR 2016 UL http://biorxiv.org/content/early/2016/02/01/038372.abstract AB Although cell cycle control is an ancient, conserved, and essential process, some core animal and fungal cell cycle regulators share no more sequence identity than non-homologous proteins. Here, we show that evolution along the fungal lineage was punctuated by the early acquisition and entrainment of the SBF transcription factor. Cell cycle evolution in the fungal ancestor then proceeded through a hybrid network containing both SBF and its ancestral animal counterpart E2F, which is still maintained in many basal fungi. We hypothesize that a viral SBF may have initially hijacked cell cycle control by activating transcription via the cis-regulatory elements targeted by the ancestral cell cycle regulator E2F, much like extant viral oncogenes. Consistent with this hypothesis, we show that SBF can regulate promoters with E2F binding sites in budding yeast.