>TIGR00442 hisS histidyl-tRNA synthetase; InterPro: IPR015807 The aminoacyl-tRNA synthetases (6.1.1. from EC) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction. These proteins differ widely in size and oligomeric state, and have limited sequence homology . The 20 aminoacyl-tRNA synthetases are divided into two classes, I and II. Class I aminoacyl-tRNA synthetases contain a characteristic Rossman fold catalytic domain and are mostly monomeric . Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices , and are mostly dimeric or multimeric, containing at least three conserved regions , , . However, tRNA binding involves an alpha-helical structure that is conserved between class I and class II synthetases. In reactions catalysed by the class I aminoacyl-tRNA synthetases, the aminoacyl group is coupled to the 2'-hydroxyl of the tRNA, while, in class II reactions, the 3'-hydroxyl site is preferred. The synthetases specific for arginine, cysteine, glutamic acid, glutamine, isoleucine, leucine, methionine, tyrosine, tryptophan and valine belong to class I synthetases; these synthetases are further divided into three subclasses, a, b and c, according to sequence homology. The synthetases specific for alanine, asparagine, aspartic acid, glycine, histidine, lysine, phenylalanine, proline, serine, and threonine belong to class-II synthetases . Histidyl-tRNA synthetase (6.1.1.21 from EC) is an alpha2 dimer that belongs to class IIa. Every completed genome includes a histidyl-tRNA synthetase. Apparent second copies from Bacillus subtilis, Synechocystis sp., and Aquifex aeolicus are slightly shorter, more closely related to each other than to other hisS proteins, and not demonstrated to act as histidyl-tRNA synthetases (see IPR004517 from INTERPRO). The regulatory protein kinase GCN2 of Saccharomyces cerevisiae (YDR283c), and related proteins from other species designated eIF-2 alpha kinase, have a domain closely related to histidyl-tRNA synthetase that may serve to detect and respond to uncharged tRNA(his), an indicator of amino acid starvation, but these regulatory proteins are not orthologous.; GO: 0000166 nucleotide binding, 0004821 histidine-tRNA ligase activity, 0005524 ATP binding, 0006412 translation, 0006427 histidyl-tRNA aminoacylation, 0005737 cytoplasm.

Probab=96.02  E-value=0.017  Score=37.41  Aligned_cols=119  Identities=24%  Similarity=0.366  Sum_probs=73.0

Q ss_pred             CCCCHHHHHHHHHHHHHHHHCCCEEEEECCCCCCCC---C-CC-CCC------CCCCCCCCHHHHHHCCCCHH-------
Q ss_conf             112124589999999875203651462033211246---4-56-645------43222221034431123854-------
Q gi|254780419|r  138 LHKNIVKRTRIINSMRCRMIAENFIECSTPILTASS---P-EG-ARD------FLVPSRVNQGSFYALPQAPQ-------  199 (622)
Q Consensus       138 ~~~~l~~Rs~i~~~~R~~l~~~gF~EveTP~L~ksT---p-eG-Ard------FlVPsR~~~g~fYALpQSPQ-------  199 (622)
T Consensus        14 ~p~~~~~~~~~~~~~~~~~~~~g~~~~~~P~~e~~~~~~~~~~~~~~~~~~~~y~f--~d~~~~~--~~lrp~~t~~~~r   89 (446)
T TIGR00442        14 LPGELVYRQWIEAKLRSVLESYGYSEIRTPIFEYTELFARGIGKSGDEVEKELYTF--KDKGGRD--LALRPELTAPVVR   89 (446)
T ss_pred             CCHHHHHHHHHHHHHHHHHHHCCCCCCCCCHHHHHHHHHHHCCCCHHHHHHHHEEE--ECCCCCE--EEECCCHHHHHHH
T ss_conf             54157899999999999997517720012114445666530253013344443012--1278841--4422200368999


Q ss_pred             HH-HHHHHC--CCHHHHEEEHHHHCCCCCC-CCCCCCCEEEEEEEEC----CCCHHHHHHHHHHHHHHHH
Q ss_conf             56-443310--5702331100110377766-5538000035654102----6899999999999999999
Q gi|254780419|r  200 QY-KQLLMA--SGFDRYFQIAPCFRDEDPR-SDRLPGEFYQLDMEMS----FVEQDDILNTMENVLRGVF  261 (622)
Q Consensus       200 ly-KQlLmv--~G~dryfqiarcFRdEd~R-~dRqp~EFTqlD~Ems----F~~~edvm~l~E~li~~i~  261 (622)
T Consensus        90 ~~~~~~~~~~~~~p~~~~~~g~~~r~e~p~~~gr~r-~f~~~~~~~~G~~~~~~~~~~~~~~~~~~~~~g  158 (446)
T TIGR00442        90 LVAENKLLLPANKPLRLYYIGPVFRYERPQLKGRYR-EFWQFGCEVIGSESPLADAEVLSLAVEGLKALG  158 (446)
T ss_pred             HHHHHHHHCCCCCCEEEEEEECHHHCCCHHHHCCHH-HHHHCCEEEECCCCCHHHHHHHHHHHHHHHHHC
T ss_conf             998754310467642432320101022412301011-332115046436652036899999999898607