Wheat-embryo ribonucleates. XV. Characterization of a fraction of RNA subject to conspicuous terminal labeling during early germination of wheat embryos

Abstract

Various techniques have been used to characterize the rapidly migrating electrophoretic components (RMEC) in an RNA fraction which is subject to conspicuous terminal labeling (mostly adenosine) when wheat embryos are pulse labeled with 3H-labeled nucleosides during early germination. Detection of terminally labeled RMEC RNA is most favoured during early germination when labeling of 3′-hydroxyl termini in preexisting RNA, catalyzed by RNA nucleotidyltransferases, is greatest in relation to nonterminal labeling of nascent RNA, catalyzed by RNA polymerases. The RMEC RNA is tenaciously associated with a fraction of high-molecular-weight RNA and it can be subdivided and classified into two fractions, RMEC-1 and RMEC-2, by electrophoresis in polyacrylamide, gel filtration through Sephadex, or assay of amino acid acceptance. The RMEC-1 RNA and bulk wheat-embryo tRNA have similar capacities to accept a wide variety of amino acids, but RMEC-2 RNA does not accept any of the amino acids tested. RMEC-2 RNA is broadly heterodisperse and one of its component polynucleotides has been identified by sequence analysis as a tridecanucleotide fragment from the 3′-hydroxyl end of 5.8S rRNA. This study was undertaken as part of a broader program in which isotopic labeling and analysis of nucleates and proteins in germinating wheat embryos have been used to detect signal events and to evaluate their physiological significance. It is concluded that conspicuous terminal labeling of RMEC RNA during early germination of wheat embryos is unlikely to be of physiological importance. However, isotopic labeling and analysis of the nucleates and proteins in germinating embryos has uncovered other signal events which appear to be of physiological importance. Discovery of the existence of a number of developmentally regulated proteins and the way in which discovery of these proteins is expected to direct the course of future investigations in the laboratory are subjects of a brief discussion.