Chloroplast sensor kinase
Chloroplast Sensor Kinase is a protein in chloroplasts of green plants and algae. In the plant Arabidopsis thaliana CSK is the product of the gene At1g67840. CSK is also found in cyanobacteria; prokaryotes from which chloroplasts evolved by endosymbiosis. CSK is an iron-sulfur protein with 3 iron and 4 sulphur atoms in its redox-active site. It has a midpoint redox potential of −15 mV at pH 8, which is consistent with its autophosphorylation communicating the redox state of the plastoquinone pool to regulation of chloroplast DNA transcription – specifically of genes for proteins at the photochemical reaction center of photosystem I. CSK and its redox regulatory function are inherited from the prokaryotic, cyanobacterial ancestor of chloroplasts. CSK is a prediction of the CoRR Hypothesis for genes in organelles. CSK is intrinsic to chloroplasts, targeted to chloroplast genes, and may have been required for the retention, in evolution, of chloroplast DNA.
