This family is in the P-loop NTPase superfamily and is found in archaea, bacteria and eukaryotes. More than one copy is sometimes found in each protein. This family includes KaiC, which is one of the Kai proteins among which direct protein-protein association may be a critical process in the generation of circadian rhythms in cyanobacteria [1].

1: Physical interactions among circadian clock proteins KaiA, KaiB and KaiC in cyanobacteria. Iwasaki H, Taniguchi Y, Ishiura M, Kondo T; EMBO J 1999;18:1137-1145. PMID:10064581