ISOLATION AND MOLECULAR PHYLOGENETIC ANALYSIS OF ACTIN CODING REGIONSFROM EMILIANIA-HUXLEYI, A PRYMNESIOPHYTE ALGA, BY REVERSE-TRANSCRIPTASE AND PCR METHODS

Reverse transcriptase and polymerase chain reaction methods were used to amplify and clone actin cDNAs from the chlorophylls a+c-containing unicellular alga, Emiliania huxleyi (Prymnesiophyta). Actins in E. hux leyi arc defined by a gene family containing at least six distinct cod ing regions that were derived from relatively recent gene duplications . Five of the coding regions (types 1, 2, and 4-6) varied only among s ynonymous codons. A nonsynonomous change in a sixth coding region (typ e 3 actin) produced a serine-to-phenylalanine replacement. The G+C com position of third positions in E. huxleyi actin genes is 98%, which co ntrasts with the mean value of 50% G+C content for first and second po sitions. Distance-matrix and parsimony analyses of actin genes identif ied the prymnesiophytes as a photosynthetic lineage that is not alread y related to other eukaryotic algal groups.