>TIGR00443 hisS_second histidyl-tRNA synthetase 2, putative; InterPro: IPR004517 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 (see IPR004516 from INTERPRO). Every completed genome includes a histidyl-tRNA synthetase. Apparent second copies from Bacillus subtilis, Synechocystis spp., 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. 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. An unusual feature is that this putative second HisS is shorter at the C-terminus. It shows greater similarity to archaeal HisS than to other bacterial HisS. There is reason by analogy to suspect this second HisS may have a function other than (or in addition to) ligating His to its tRNA: the protein kinase DGCN2 of Drosophila has a C-terminal domain related to HisS that appears to detect uncharged tRNA(his), an indicator of amino acid starvation, and respond by phosphorylating eIF-2alpha.; GO: 0000105 histidine biosynthetic process, 0005737 cytoplasm.

Probab=100.00 E-value=2.9e-37 Score=261.15 Aligned_cols=385 Identities=24% Similarity=0.348 Sum_probs=275.4 Q ss_pred CCCCCCCCCCCCCHHHHHHHHHHHHHHHHHHHHCCCEEEECCCHHHHHHHHCCCCCCCCCCCCEEEEECCC-CCEEEECC Q ss_conf 71037998765886689999999999999999859848016520228875202675543332216898699-98899988 Q gi|254780928|r 7 LRAELPRGFADCPTKEIRIRNRILDSIRNIYENYGFDPIETPLLEYSDSLGKFLPDEDRPNKGVFSLQDDD-GQWISLRY 85 (496) Q Consensus 7 ~~~~~P~G~~D~~p~~~~~~~~i~~~l~~~f~~~G~~~I~tP~lE~~~~~~~~~~~~~~~~k~~y~f~D~~-g~~l~LRp 85 (496) T Consensus 1 ~~~~~~~g~~~~~~~~~~~~~~~~~~~~~~~~~~g~~~~~~~~~~~~~~~~~~~~~---~~~~~~~~~d~~~~~~~~l~~ 77 (414) T TIGR00443 1 FKFEPPAGERDLLPGEYELKKKINKKLTDLFDKWGYQFIETSTLEWYDTLGLGGAI---GAKELIKLLDSGTGGTLGLRP 77 (414) T ss_pred CCCCCCCCHHHHHHHHHHHHHHHHHHHHHHHHHHCCHHHCCCCCCHHHHHHHCCCC---CHHHHHEEECCCCCCCEEECC T ss_conf 96665554034445677788899889999998614012101322112333210110---000210000034554021122 Q ss_pred CCHHHHHHHHHHHHHHCCCCHHHHHHHHHHCCC-CCCCCCCCCCCCCCHHHHHCCCHHHHHHHHHHHHHHHHHCCCCCCC Q ss_conf 883899999995112055411233101333025-8764442111110001210000245788999999999751888777 Q gi|254780928|r 86 DLTAPLARYVAENFDTIVFPCRTYRIGPVFRNE-KHGPGRFRQFIQCDVDNVGSSAETADAEMCMMMADTLEAVGIKRND 164 (496) Q Consensus 86 DlT~~~aR~~~~~~~~~~~p~k~yy~g~vfR~e-~p~~Gr~REf~Q~g~eiiG~~~~~~DaEii~l~~~~l~~lgl~~~~ 164 (496) T Consensus 78 ~~~~~~~~~~~~~~~~~~~p~~~~~~~~~~~~~p~~~~g~~~~~~~~g~~l~~~~~~~~d~~~~~~~~~~l~~~gl~--~ 155 (414) T TIGR00443 78 DLTGPIARAAVSKLLDNGLPERVGYFANVFRLPPEGYGGRGFEFLQAGVELLGDGGVLADAEVLLLLTGCLKSLGLA--D 155 (414) T ss_pred CCHHHHHHHHHHHHHHCCCCHHHHHHHHHHCCCCCCCCCCCCHHHHHHHHHHCCCCCHHHHHHHHHHHHHHHHCCCH--H T ss_conf 20146889999887623661133222111026753345654123442023210343012578999999988631501--3 Q ss_pred CEEECCCCHHHHHHHHHHCCCHHHHHHHHHHHHHHHHHCCCCCHHHHHHHHHHCCCCHHHHHHCCCCCCHHHHHHHHHHH Q ss_conf 11303660558999998325603564334555333220012896789986210165003555304899977899888740 Q gi|254780928|r 165 YHIGINNRKILDGILEKIGLHGDDKLNERLIVLRAIDKLDKFGLQGVKLLLGEGRTDNSGDFTKGANLTSEQIDIMVSFL 244 (496) Q Consensus 165 ~~I~in~~~il~~il~~lgi~~~~~~~~~~~~~~~idkl~k~~~~~~~~~l~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 244 (496) T Consensus 156 ~~~~~~~~g~~~~~~~~~~~~~~----~~~~~~~~~~~~~~~~~---------------~~~~~~~p~~~~~~~~~~~~~ 216 (414) T TIGR00443 156 WKLILGHAGLARALLDELPGLLE----RAAFLRRCLEELDYVGG---------------REHVKSLPLPDEDKNDLLELL 216 (414) T ss_pred HHHHHHCCHHHHHHHHHHHHHHH----HHHHHHHHHHHHHHHHH---------------HHHHHHCCCCCHHHHHHHHHH T ss_conf 45554101046788775333456----77888888888776543---------------344531577402467888888 Q ss_pred CCCC--HHHHHHHHHHHCCCHHHHHHHHHHHHHHHHHHHC--CCCCCCCCCCHHHCCCCCCCCCEEEEEEECCCCCCCCC Q ss_conf 4785--6889989986035732588899999999998750--88844300110100122123412489985466677676 Q gi|254780928|r 245 SIDL--EKSMHELYELVKGTIAGEKGFNELVVISELVRKS--GYNSNRIKISSTIVRGLEYYTGCVYEAILGFPVMNEKQ 320 (496) Q Consensus 245 ~~~~--~~~~~~l~~~~~~~~~~~~~l~~l~~i~~~l~~~--gv~~~~i~~Dl~lvRgLdYYTG~vFE~~~~~~~~~~~~ 320 (496) T Consensus 217 ~~~~~~~~~~~~~~~-~~~~~~~~~~~d~l~~l~~~~~~~gdg~~-~~~~~dl~~~~~~~~~~g~~~~~~~~-------- 286 (414) T TIGR00443 217 ELRGTGPEVLGRLEK-LDLEGEGLGLVDELLALGDLLEDFGDGPT-ENLALDLGWVRPFPYYTGVLFEVYAL-------- 286 (414) T ss_pred HHCCCHHHHHHHHHH-HHHHHHHHHHHHHHHHHHHHHHHHCCCCC-HHHHHHHHHHCCCCHHHHHHHHHHHH-------- T ss_conf 740422788766654-43211112368999999999986157731-12322123312453023366655441-------- Q ss_pred CCCCEEEECCCCCCCCCCCCCCCCC--CCCCEEEECCHHHHHHHHHCCCCCCCCCCCCEEEEEEECCCHHHHHHHHHHHH Q ss_conf 6631011003232355211123456--77421331101689999973687766555771489982697689999999999 Q gi|254780928|r 321 KPVVFGSVGGGGRYDGLVSRFKGQN--VPATGFSIGISRLIVALKSLESSTNNIKEMGPVLITTMDHDSDSLSKYQMYTQ 398 (496) Q Consensus 321 ~~~~~~aI~~GGRYD~L~~~f~~~~--~pavGfaigverl~~~l~~~~~~~~~~~~~~~v~V~~~~~~~~~~~~~~~ia~ 398 (496) T Consensus 287 ~~~~c~~~~~gg~~~~l~~~~~~~~~~~p~~g~~~~~~~l~~~l~~~~~~p~-~~~~~d~~~~--~~~~~--~~~~~~~~ 361 (414) T TIGR00443 287 KAGNCFVLGGGGRYDKLLGHYGPPYQSFPATGFGLNLERLLECLPKLGTLPT-EPCPIDYLVC--PKDDK--AEGLALAD 361 (414) T ss_pred CCCCEEEEECCCCHHHHHHHCCCCHHCCCCCCCHHHHHHHHHHHHHCCCCCC-CCCCCCEEEE--CCHHH--HHHHHHHH T ss_conf 2575367506741234554316300014666520228889998752166665-4233322662--33023--45667776 Q ss_pred HHHHCCCE--EEEEECCCCCHHHHHHHHHHCCCC Q ss_conf 99987983--999718999988999999877998 Q gi|254780928|r 399 MLRTAGIR--AEMFLGSSKNFGNQLKYADRRNCP 430 (496) Q Consensus 399 ~Lr~~Gi~--~e~~~~~~~sl~~~~~~A~~~g~~ 430 (496) T Consensus 362 ~~~~~~~~pd~~~~~~~~~~~~~~~~~~~~~~~~ 395 (414) T TIGR00443 362 AERLKGKKPDVGLELLLGGGLEPELLKAFAKGFK 395 (414) T ss_pred HHHHHCCCCCCHHHHHHCCCCCHHHHHHHHHHHH T ss_conf 7875035764111111113420467777664334

HHsearch alignment for GI: 254780928 and conserved domain: TIGR00443