Regulation of protein synthesis during spore germination in Dictyostelium discoideum

Spore germination in the slime mold Dictyostelium 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, we labeled activated spores with [35S]methionine at 1-hr intervals during germination, until amebas emerged (at 3 hr). The labeled proteins were resolved by two-dimensional polyacrylamide gel electrophoresis. Six classes of proteins were distinguished, depending on the time of onset and duration of their synthesis: (i) proteins made only during the first hour of germination, (ii) proteins made during the second hour, (iii) proteins made during the third hour, (iv) those synthesized only between 1 and 3 hr after activation, (v) peptides made only between 0 and 2 hr after activation, and (vi) 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 pattern of protein synthesis that occurred during the different stages of germination were attributable to the presence or absence of translatable mRNA. It is concluded that the synthesis of a majority of the proteins during spore germination is transcriptionally controlled.