{PDOC00161}
{PS00178; AA_TRNA_LIGASE_I}
{BEGIN}
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* Aminoacyl-transfer RNA synthetases class-I signature *
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Aminoacyl-tRNA  synthetases (EC 6.1.1.-) [1] are  a  group  of  enzymes  which
activate amino acids and transfer them to specific tRNA molecules as the first
step in protein biosynthesis. In  prokaryotic organisms  there  are  at  least
twenty different types  of aminoacyl-tRNA synthetases,  one for each different
amino acid. In eukaryotes  there are  generally two aminoacyl-tRNA synthetases
for  each  different amino  acid: one cytosolic form and a mitochondrial form.
While all these  enzymes have  a  common  function, they are widely diverse in
terms of subunit size and of quaternary structure.

A few years ago it was found [2] that several aminoacyl-tRNA synthetases share
a  region  of  similarity in  their   N-terminal  section,  in  particular the
consensus tetrapeptide His-Ile-Gly-His ('HIGH') is  very  well  conserved. The
'HIGH' region has been shown [3] to be part of the adenylate binding site. The
'HIGH' signature has been found in the aminoacyl-tRNA synthetases specific for
arginine, cysteine, glutamic acid, glutamine, isoleucine, leucine, methionine,
tyrosine,  tryptophan,  and   valine.  These  aminoacyl-tRNA  synthetases  are
referred to as class-I synthetases [4,5,6] and seem to share the same tertiary
structure based on a Rossmann fold.

-Consensus pattern: P-x(0,2)-[GSTAN]-[DENQGAPK]-x-[LIVMFP]-[HT]-[LIVMYAC]-G-
                    [HNTG]-[LIVMFYSTAGPC]
-Sequences known to belong to this class detected by the pattern: ALL,  except
 for Cys-tRNA ligases and some other sequences.
-Other sequence(s) detected in Swiss-Prot: 57.

-Note: In position 8 of the  pattern His is present in all tRNA-synthetases of
 class-I  except in some bacterial tryptophanyl-tRNA synthetases  which have a
 Thr in that position.

-Last update: November 1997 / Pattern and text revised.

[ 1] Schimmel P.
     "Aminoacyl tRNA synthetases: general scheme of structure-function
     relationships in the polypeptides and recognition of transfer RNAs."
     Annu. Rev. Biochem. 56:125-158(1987).
     PubMed=3304131; DOI=10.1146/annurev.bi.56.070187.001013
[ 2] Webster T., Tsai H., Kula M., Mackie G.A., Schimmel P.
     "Specific sequence homology and three-dimensional structure of an
     aminoacyl transfer RNA synthetase."
     Science 226:1315-1317(1984).
     PubMed=6390679
[ 3] Brick P., Bhat T.N., Blow D.M.
     "Structure of tyrosyl-tRNA synthetase refined at 2.3 A resolution.
     Interaction of the enzyme with the tyrosyl adenylate intermediate."
     J. Mol. Biol. 208:83-98(1989).
     PubMed=2504923
[ 4] Delarue M., Moras D.
     "The aminoacyl-tRNA synthetase family: modules at work."
     BioEssays 15:675-687(1993).
     PubMed=8274143
[ 5] Schimmel P.
     "Classes of aminoacyl-tRNA synthetases and the establishment of the
     genetic code."
     Trends Biochem. Sci. 16:1-3(1991).
     PubMed=2053131
[ 6] Nagel G.M., Doolittle R.F.
     "Evolution and relatedness in two aminoacyl-tRNA synthetase
     families."
     Proc. Natl. Acad. Sci. U.S.A. 88:8121-8125(1991).
     PubMed=1896459

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