Together with COR27, involved in central circadian clock regulation and in flowering promotion, by binding to the chromatin of clock-associated evening genes TOC1, PRR5, ELF4 and cold-responsive genes in order to repress their transcription (PubMed:27837007, PubMed:27990760). Negative regulator of freezing tolerance (PubMed:27837007). Regulated by the circadian clock at warm growth temperatures as direct targets of CCA1, with highest levels from noon to dusk (PubMed:27837007, PubMed:27990760). Repressed by CCA1 at the transcription level via chromatin binding and in a temperature-dependent way (PubMed:27837007, PubMed:27990760). Induced by cold (PubMed:12172015, PubMed:16121258, PubMed:27837007). Induced by abscisic acid (ABA) (PubMed:17304219). Transcription is repressed by blue and red lights, but induced by darkness; by contrast, present at low levels in darkness but accumulates in blue light (at protein level) due to transcription auto-repression (PubMed:27837007). Period lengthening of various circadian output rhythms and affected central clock gene expression (PubMed:27837007). Derepressed expression of circadian-regulated and cold-responsive genes (PubMed:27990760). Delayed flowering under long days conditions, and slightly in short days (PubMed:27837007). Increased freezing tolerance (PubMed:27837007).