Variations in Attachment of a Cysteine Conjugate to Soluble Ribonucleic Acid
Edsel T. Bucovaz 1, John C. Morrison 1, and John L. Wood 1
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1 From the Department of Biochemistry, University of Tennessee Medical Units, Memphis, Tennessee 38103
A cell-free system was prepared from rat liver which catalyzed the incorporation of cysteine and the analogue of cysteine, S-(1,2,3,4-tetrahydro-2-hydroxy-1-naphthyl)-l-cysteine, into ribosomal protein. Fractionation of this system with (NH4)2SO4 resulted in the separation of the cysteinyl soluble ribonucleic acid synthetase (cysteinyl-sRNA synthetase) from the aminoacyl-sRNA synthetases, presumably those for valine and isoleucine, that catalyzed the transfer of the S-substituted cysteine analogue to sRNA. Furthermore, in incubation media that contained the synthetases for cysteine and analogue transfer, an excess of unlabeled cysteine did not inhibit aminoacylation of sRNA by the 3H- or 35S-labeled analogue. However, the addition of either valine or isoleucine produced a marked inhibition of the transfer of radioactive tetrahydrohydroxynaphthylcysteine to sRNA. These observations were consistent with the concept that valyl- and isoleucyl-sRNA synthetases and their respective transfer RNAs are operational for the cysteine analogue. In contrast, the reaction of 1,2-epoxy-1,2,3,4-tetrahydronaphthalene with cysteinyl-sRNA resulted in formation of the analogue attached to the cysteine transfer RNA. The incorporation of (1,2,3,4-tetrahydro-2-hydroxy-1-naphthyl)-l-cysteine into protein should occur in a position determined by the species of sRNA that is acting as the transfer agent.
Submitted on February 7, 1966
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