HUMAN ASPARAGINYL-TRANSFER-RNA SYNTHETASE - MOLECULAR-CLONING AND THEINFERENCE OF THE EVOLUTIONARY HISTORY OF ASX-TRANSFER-RNA SYNTHETASE FAMILY

We have cloned and sequenced a cDNA encoding human cytoplasmic asparag inyl-tRNA synthetase (AsnRS), The N-terminal appended domain of 112 am ino acid represents the signature sequence for the eukaryotic AsnRS an d is absent from archaebacterial or eubacterial enzymes. The canonical ortholog for AsnRS is absent from most archaebacterial and some eubac terial genomes, indicating that in those organisms, formation of aspar aginyl-tRNA is independent of the enzyme. The high degree of sequence conservation among asparaginyl- and aspartyl-tRNA synthetases (AsxRS) made it possible to infer the evolutionary paths of the two enzymes. T he data show the neighbor relationship between AsnRS and eubacterial a spartyl-tRNA synthetase, and support the occurrence of AsnRS early in the course of evolution, which is in contrast to the proposed late occ urrence of glutaminyl-tRNA synthetase.