Cyanobacteria are the only prokaryotes known thus far possessing regulation of physiological functions with approximate daily periodicity, or circadian rhythms, that are controlled by a cluster of three genes, kaiA, kaiB, and kaiC. Here we demonstrate considerably higher genetic polymorphism and extremely rapid evolution of the kaiABC gene family in a filamentous cyanobacterium, Nostoc linckia, permanently exposed to the acute natural environmental stress in the two microsite evolutionary models known as "Evolution Canyons," I (Mount Carmel) and II (Upper Galilee) in Israel. The family consists of five distinct subfamilies (kaiI-kaiV) comprising at least 20 functional genes and pseudogenes. The obtained data suggest that the duplications of kai genes have adaptive significance, and some of them are evolutionarily quite recent (≈80,000 years ago). The observed patterns of within- and between-subfamily polymorphisms indicate that positive diversifying, balancing, and purifying selections are the principal driving forces of the kai gene family's evolution.
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - 19 Feb 2002|
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