Alternate copies of D1 are used by cyanobacteria under different environmental conditions.

All cyanobacteria sequenced to date have multiple psbA genes, encoding the D1 protein. Some of these psbA genes have a series of mutations that would seem to render D1 incapable of binding the Mn(4)CaO(5) metallocluster (Murray, Photosynth Res 110(3):177-184, 2012). Nonetheless, these genes are expressed under specific environmental conditions, such as during N(2) fixation in unicellular diazotrophs of the genes Cyanothece. These genes emphasize the clever way that cyanobacteria have learned to deal with a constantly changing environment.