Cell-specific expression of a profilin gene family.

Profilin is a ubiquitous eukaryotic protein that inhibits actin polymerization. We cloned and sequenced the two profilin genes from the acellular slime mold Physarum polycephalum. The genes, proA and proP, each contain two introns. Primer extension experiments showed two possible transcription start sites in the profilin A gene and one start site in the profilin P gene. The profilin A mRNA has two polyadenylation sites, which yield mRNAs of about 600 and 500 nucleotides. The profilin P mRNA has a single polyadenylation site. The protein sequences were deduced from cDNA nucleotide sequencing. The profilin A and profilin P proteins contain 125 amino acids and are 66% identical in sequence. They show sequence similarity to Acanthamoeba (approximately 54%), yeast (approximately 46%), mouse (approximately 22%), calf (approximately 21%), and human (approximately 21%) profilins. The presence of the profilin A and profilin P mRNAs was studied throughout the life cycle. Profilin A mRNA was found in amebas, encysted amebas, and mature spores. The profilin P mRNA was present in plasmodia and spherulating plasmodia. Most cell types of P. polycephalum contain either the amebal or the plasmodial profilin mRNA, and no cell contains both mRNAs. This is the first evidence for developmental regulation of profilin isoforms.