Also in the KaiC family is RadA/Sms, a highly conserved eubacterial protein that shares sequence similarity with both RecA strand transferase and lon protease.

The RadA/Sms family are probable ATP-dependent proteases involved in both DNA repair and degradation of proteins, peptides, glycopeptides.

[2][5] KaiC belongs to a larger family of proteins; it performs autophosphorylation and acts as its own transcriptional repressor.

In a 1993 experiment, they used a luciferase reporter inserted into the genetically tractable Synechococcus sp., which was grown in a 12:12 light-dark cycle to ensure “entrainment”.

(1) The circadian oscillators in eukaryotes that have been studied function using a negative feedback loop in which proteins inhibit their own transcription in a cycle that takes approximately 24 hours.

They did this by adding KaiA, KaiB, KaiC, and ATP into a test tube in the approximate ratio recorded in vivo.

They then measured the levels of KaiC phosphorylation and found that it demonstrated circadian rhythmicity for three cycles without damping.

These results led them to conclude that KaiC phosphorylation is the basis for circadian rhythm generation in Synechococcus.

(2)(3) The primitiveness and simplicity make the KaiC phosphorylation model invaluable to circadian rhythm research.