Human phenylalanyl-tRNA synthetase: Cloning, characterization of the deduced amino acid sequences in terms of the structural domains and coordinatelyregulated expression of the alpha and beta subunits in chronic myeloid leukemia cells

Unlike the catalytic alpha-subunit, the beta-subunit of heterodimeric (alph a beta)(2) phenylalanyl-tRNA synthetase (PheRS) has no invariant functional amino acids directly involved in the aminoacylation process as it is evide nt from the crystal structure of the T. thermophilus enzyme complexed with tRNA(Phe). Having no catalytic function, the prokaryotic beta-subunit compr ises OB-, RNP-, SH3-, and DNA-binding-like domains involved in a variety of biological functions in other proteins. It was shown that the mRNA of the human alpha-subunit overexpressed in the tumorigenic versus the nontumorige nic variant of the same acute-phase chronic myeloid leukemia cell line (CML ). We cloned, sequenced, and expressed human PheRS. The layout of the human sequence indicates that the general tRNA binding mode and anticodon recogn ition differ between prokaryotes and eukaryotes for the phenylalanine syste m. Northern blot hybridization analysis from malignant and normal human tis sues enabled us to assess the relative expression levels of the alpha- and beta-subunits independently, in view of the additional cellular role propos ed for the beta-subunit in tumorigenic events. The levels of mRNA correspon ding to the alpha- and beta-subunits were remarkably similar in all cell ty pes and tissues examined, thus indicating the implication of the entire (al pha beta)(2) heterodimer in tumorigenic events, (C) 1999Academic Press.