Genomic and cDNA actin sequences from a virulent strain of Entamoeba histolytica.

Invasiveness of Entamoeba histolytica strains that cause acute amoebiasis is characterized by aggressive behavior associated with cell motility and actin function. Analysis of actin genes from E. histolytica was initiated by devising methods for the isolation of biologically active nucleic acids, which allowed the preparation of cDNA and genomic DNA libraries. E. histolytica actin-encoding cDNAs and genomic clones have been isolated from libraries prepared from the virulent HM1:IMSS strain using a heterologous actin probe. Nucleotide sequence analysis of three independent cDNA clones and one genomic clone reveals a highly unusual codon bias and the absence of intervening sequences in E. histolytica actin. The coding sequence of the genomic clone is identical to that of two of the three cDNA clones. These represent at least two distinct mRNAs differing only by five silent changes in the protein coding sequence. Multiple genomic copies of the actin gene can be detected by Southern hybridization. E. histolytica actin exhibits a higher degree of homology to cytoplasmic than to muscle actin. Although the protein has been shown not to bind DNase I, the inferred amino acid sequence indicates conservation of all residues implied to participate in this binding.