Molecular cloning of a rac family protein kinase and identification of a serine/threonine protein kinase gene family of Entamoeba histolytica.

Eleven Entamoeba histolytica protein-serine/threonine-kinase gene segments were identified using the polymerase chain reaction (PCR) and degenerate oligonucleotide primers to conserved amino acids in subdomains VI and VIII of the catalytic domain of protein-serine/threonine kinases. These ameba gene segments were homologous to myosin light chain kinases, protein kinase C, phosphorylase b kinase, and kinases that regulate glucose repression in yeast and cell growth in mammalian cells. One of these PCR products, which was homologous to the Dictyostelium discoideum protein kinase 2, was used to identify a full-length protein-serine/threonine-kinase gene (Eh rac1) from an E. histolytica genomic library. The open reading frame of Eh rac1 was 409 amino acids long (encoding a 47-kDa protein) and included an amino terminal segment containing 87 mostly charged and polar amino acids and a 322-amino acid carboxyl terminal segment containing the catalytic domain. The catalytic domain of Eh rac1 was homologous to the rac family of protein-serine/threonine-kinases, which are related to cAMP-dependent protein kinases and protein kinase Cs. Southern blots of ameba DNA showed that the Eh rac1 gene was present as a single copy in all strains tested, however pathogenic amebae expressed four times more Eh rac1 mRNAs than did nonpathogenic amebae. These studies suggest that E. histolytica, a primitive unicellular eukaryote, has a complex protein kinase family.