Paramecium tetraurelia encodes unconventional actin containing short introns

The polymerase chain reaction was used to amplify and clone an actin gene fragment from Paramecium tetraurelia. This DNA fragment was 1,138 bp long, more than 96% of the actin coding sequence, and contained four in-frame UAA codons and two small introns located at positions unique in the actin intron catalogue. This is the first report for the phylum Ciliophora of an actin gene containing introns. The deduced amino acid sequence of this actin fragment shared 58-77% identity with other actins. When compared with rabbit alpha-muscle actin, similarities were observed mainly in subdomains 1 and 3, whereas subdomains 2 and 4 appeared to be more divergent.