Heterogeneity of Entamoeba histolytica rac genes encoding p21(rac) homologues

Entamoeba histolytica (Eh), the parasite that causes amebic dysentery, is the only protozoan that phagocytoses bacteria, epithelial cells and red blood cells. Numerous low-molecular-weight GTP-binding proteins, called p21(rac), are implicated in signal transduction and actin polymerization during phagocytosis by macrophages and Dictyostelium discoideum (Dd). Here, molecular cloning techniques were used to obtain four Eh rac genes that encoded putative p21(rac), as well as segments of two Eh rac pseudogenes. The predicted Eh p21(rac), which share 55-81% amino acid (aa) identities with each other, include one that closely resembles the p21(rac1) of man, Dd, Drosophila melanogaster and Caenorhabditis elegans; two that resemble the p21(racC) of Dd; and one that is unique. An alignment of the Eh rac ORF with other rac family proteins reveals multiple aa that distinguish p21(rac1), p21(racC) and p21(cdc42). We conclude that the Eh genes encoding amebic p21(rac), which are the first identified from a protozoan parasite, are numerous and heterogeneous.