Regulation of protein synthesis during spore germination in Dictyostelium discoideum.

Abstract

Spore germination in the slime mold D. discoideum is a particularly suitable paradigm for studying the regulation of gene expression because developmentally regulated changes in both protein and mRNA synthesis occur during the synchronous transition from dormant spore to growing ameba. To investigate the regulation of protein synthesis during germination, activated spores were labeled with [35S]methionine at 1-h intervals during germination, until amebas emerged (at 3 h). The labeled proteins were resolved by 2-dimensional polyacrylamide gel electrophoresis. Six classes of proteins were distinguished, depending on the time of onset and duration of their synthesis: proteins made only during the 1st h of germination, proteins made during the 2nd h, proteins made during the 3rd h, those synthesized only between 1 and 3 h after activation, peptides made only between 0 and 2 h after activation, and proteins that were made throughout germination. mRNA isolated from dormant spores and from spores at different stages of germination was translated in a wheat germ cell-free protein-synthesizing system, and the proteins made in vitro were compared to those synthesized in vivo. The majority of the changes in the patern of protein synthesis that occurred during the different stages of germination were attributable to the presence or absence of translatable mRNA. The synthesis of a majority of the proteins during spore germination is transcriptionally controlled.