THE HUMAN GENE ENCODING TRYPTOPHANYL-TRANSFER-RNA SYNTHETASE - INTERFERON-RESPONSE ELEMENTS AND EXON-INTRON ORGANIZATION

Recently, we cloned and sequenced the cDNA encoding human tryptophanyl-tRNA synthetase (hWRS) [Frolova et al., Gene 109 (1991) 291-296]. Independently, it has been shown that this protein is induced by interferons (IFN) gamma and alpha [Fleckner et al., Proc. Natl. Acad. Sci. USA 88 (1991) 11520-11524; Rubin et al., J. Biol. Chem. 266 (1991) 24245-24248]. This unusual feature of a housekeeping enzyme raises the problem of how the gene is regulated. Since at present the genomic structure of hWRS is unknown, this issue remains unsolved. Here, the exon-intron organization of hWRS has been deciphered. This gene consists of at least 12 exons that span more than 35 kb of DNA. At least two alternative noncoding exons precede ten coding exons. Upstream from the first exon, two GGAAAN(N/-)GAAA sequences, which are considered to be IFN-stimulating response elements (ISRE), have been revealed. The same consensus was also found in the intron region in close vicinity to the 5' end of the second exon. Thus, the IFN-stimulated synthesis of hWRS is presumably due to gene activation at the transcriptional level. Alignment of hWRS amino acid sequences has shown that exons V to XI of hWRS encode regions of structural similarity with bacterial WRS, whereas the N-terminal portion of the protein encoded by exons II to IV exhibits no homology with bacterial WRS. The enzymatically active 'core' enzyme generated by limited proteolysis [Lemaire et al., Eur. J. Biochem. 51 (1975) 237-252; Prassolov et al., Biochim. Biophys. Acta 378 (1975) 92-106; Epely et al., Eur. J. Biochem. 61 (1976) 139-146; Scheinker et al., Nucleic Acids Res. 7 (1979) 625-637] is presumably encoded by exons V to XI. It is concluded that mammalian WRS is composed of two structurally and functionally different domains encoded by the 5' and 3' portions of its gene.