S6 ribosomal protein phosphorylation and translation of stored mRNA in maize.

This article focuses on the effect that S6 ribosomal protein phosphorylation might have in regulating mRNA translation. Maize axes of either 4 or 14 h of germination were pulse-labelled for 1 h with [32P]-orthophosphate. Analysis of their ribosomal proteins by gel electrophoresis and autoradiography showed distinctive levels of S6 ribosomal protein 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 [35S]-methionine. The [35S]-proteins, resulting from stored mRNA translation, when analysed by 2-D-gel electrophoresis and fluorography revealed distinctive [35S]-protein patterns. In vitro translation of stored mRNA on ribosomes from either 4 or 14 h germinated-maize axes produced different [35S]-protein patterns. Further, addition of 7methyl-GTP-Sepharose to the translation system showed differential cap-dependent protein synthesis inhibition depending on the set of ribosomes tested. It is concluded that translation of stored mRNA in germinating maize axes is at least partially regulated by a mechanism that involves S6 ribosomal protein phosphorylation.