S6 RIBOSOMAL-PROTEIN PHOSPHORYLATION AND TRANSLATION OF STORED MESSENGER-RNA IN MAIZE

This article focuses on the effect that S6 ribosomal protein phosphory lation might have in regulating mRNA translation. Maize axes of either 4 or 14 h of germination were pulse-labelled for 1 h with [P-32]-orth ophosphate. Analysis of their ribosomal proteins by gel electrophoresi s and autoradiography showed distinctive levels of S6 ribosomal protei n phosphorylation for both ribosomal sets. Axes at these two stages of germination were treated with alpha-amanitin to ensure transcription inhibition and pulse-labelling with [S-35]-methionine, The [S-35]-prot eins, resulting from stored mRNA translation, when analysed by 2-D-gel electrophoresis and fluorography revealed distinctive [S-35]-protein patterns. In vitro translation of stored mRNA on ribosomes from either 4 or 14 h germinated-maize axes produced different [S-35]-protein pat terns. Further, addition of (7)methyl-GTP-Sepharose to the translation system showed differential cap-dependent protein synthesis inhibition depending on the set of ribosomes tested. It is concluded that transl ation of stored mRNA in germinating maize axes is at least partially r egulated by a mechanism that involves S6 ribosomal protein phosphoryla tion.