Selective gene expression during sporulation of Physarum polycephalum

The two-dimensional gel electrophoresis of polypeptides synthesized in vitro from poly(A)+ RNA showed that mRNA populations change during sporulation of Physarum polycephalum. The differential hybridization of a cDNA library prepared from poly(A)+ RNA isolated from sporulating cells revealed that of 846 clones, 64 corresponded to sporulation-specific mRNAs. Further analysis demonstrated that these clones contained seven different sequences: three abundant sequences composing 3.2, 1.8, and 1.2% of the library and four other less abundant sequences. It is probable that all the major mRNAs specifically expressed in early stages of sporulation were identified. The most abundant mRNA from this group coded for a hydrophobic protein that contained a signal peptide. This protein is 47% similar to another Physarum protein, which was encoded by the most abundant plasmodium-specific mRNA. The plasmodial mRNA was degraded during sporulation and was replaced by the sporulation mRNA. These two proteins are thus encoded by members of a gene family whose expression is developmentally regulated.