Mammalian seryl-tRNA synthetase associates with mRNA in vivo and has homology to elongation factor 1 alpha.

Previous work in our laboratories (Slobin, L. I., and Greenberg, J.R. (1988) Eur. J. Biochem. 173, 305-310) showed that messenger ribonucleoprotein (mRNP) particles possess a polypeptide component of approximately 62 kDa that appears to share a common epitope with eucaryotic elongation factor 1 alpha (EF-1 alpha). We report here that the previously unidentified mRNP constituent corresponds to seryl-tRNA synthetase (SerRS). Furthermore, we show that SerRS contains a sequence motif that is shared by both EF-1 alpha and glutaminyl-tRNA synthetase. We also find that the association of SerRS with mRNA depends on the functional state of the latter. Our data suggest that SerRS may participate directly in the initiation phase of protein synthesis.