InterPro domain: IPR015807

Histidine-tRNA ligase (also known as histidyl-tRNA synthetase) ( 6.1.1.21 ) is an alpha2 dimer that belongs to class IIa. Every completed genome includes a histidine-tRNA ligase. Apparent second copies from Bacillus subtilis, Synechocystis sp. (strain PCC 6803), and Aquifex aeolicus are slightly shorter, more closely related to each other than to other hisS proteins, and not demonstrated to act as histidine-tRNA ligases (see IPR004517 ). Theregulatory protein kinase GCN2 of Saccharomyces cerevisiae (YDR283c), and related proteins from other species designated eIF-2 alpha kinase, have a domain closely related to histidine-tRNA ligase that may serve to detect and respond to uncharged tRNA(his), an indicator of amino acid starvation, but these regulatory proteins are not orthologous.