Selenium metabolism in Drosophila - Characterization of the selenocysteinetRNA population

The selenocysteine (Sec) tRNA population in Drosophila melanogaster is amin oacylated with serine, forms selenocysteyl-tRNA, and decodes UGA. The K-m o f Sec tRNA and serine tRNA for seryl-tRNA synthetase is 6.67 and 9.45 nM, r espectively. Two major bands of Sec tRNA were resolved by gel electrophores is, Both tRNAs were sequenced, and their primary structures were indistingu ishable and colinear with that of the corresponding single copy gene. They are 90 nucleotides in length and contain three modified nucleosides, 5-meth ylcarboxymethyluridine, N-6-isopentenyladenosine, and pseudouridine, at pos itions 34, 37, and 55, respectively. Neither form contains 1-methyladenosin e at position 58 or 5-methylcarboxymethyl-2'-O-methyluridine which are char acteristically found in Sec tRNA of higher animals. We conclude that the pr imary structures of the two bands of Sec tRNA resolved by electrophoresis a re indistinguishable by the techniques employed and that See tRNAs in Droso phila may exist in different conformational forms. The Sec tRNA gene maps t o a single locus on chromosome 2 at position 47E or F, To our knowledge, Dr osophila is the lowest eukaryote in which the Sec tRNA population has been characterized to date.