Isolation and molecular phylogenetic analysis of actin-coding regions from 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. huxleyi are defined by a gene family containing at least six distinct coding regions that were derived from relatively recent gene duplications. Five of the coding regions (types 1, 2, and 4-6) varied only among synonymous codons. A nonsynonomous change in a sixth coding region (type 3 actin) produced a serine-to-phenylalanine replacement. The G + C composition of third positions in E. huxleyi actin genes is 98%, which contrasts with the mean value of 50% G + C content for first and second positions. Distance-matrix and parsimony analyses of actin genes identified the prymnesiophytes as a photosynthetic lineage that is not already related to other eukaryotic algal groups.