CLONING AND CHARACTERIZATION OF CDNA-ENCODING THE RABBIT TRANSFER-RNA-GUANINE TRANSGLYCOSYLASE 60-KILODALTON SUBUNIT

Eukaryotes synthesize queuosine (nucleoside Q) by the irreversible bas e-for-base exchange of queuine (Q base) for guanine at tRNA position 3 4, a reaction catalyzed by tRNA-guanine transglycosylase (TGT). The ph ysiological role of Q remains unknown but the tRNA of tumor cells ofte n is undermodified with respect to Q. Toward an understanding of the f unction of Q in normal and neoplastic cells we have isolated and chara cterized the cDNA for rabbit TGT. Rabbit erythrocyte TGT was reported previously to be a dimer of 60- and 43-kDa subunits (N. K. Howes and W . R. Farkas, 1978, J. Biol. Chem. 253, 9082-9078). Here we present the cDNA sequence for the apparent 60-kDa subunit; it contains an open re ading frame encoding a 493-residue protein. The rabbit TGT 60-kDa subu nit shares significant sequence similarity with the deubiquitinating e nzyme family (F. R. Papa and M. Hochstrasser, 1993, Nature 366, 313-31 9), especially with sequence elements that include conserved Cys and H is residues. (C) 1996 Academic Press, Inc.