Abstract
Both centromeric alpha-satellite sequences as well as centromeric protein A (CENP-A) are highly variable in eukaryotes. CENP-A, a histone H3 variant, is thought to act as the epigenetic "mark" for assembly of centromeric proteins. While most of the histone fold domain (HFD) of the CENP-A is fairly well conserved, a portion of this HFD as well as the N-terminal tail show adaptive variation in both plants and animals. Such variation may establish reproductive barriers that may lead to speciation. The family Percidae contains over 200 species most of which are within the subfamily Etheostomatinae. This subfamily represents a species rich radiation of freshwater fishes in North America and these species exhibit both allopatric and sympatric distributions. In order to study the evolution of CENP-A in percid fish species, we have isolated and characterized the CENP-A gene from Etheostoma tallapoosae by PCR based gene walking. As a result of this study we have demonstrated that the Tallapoosa darter CENP-A gene HFD sequences can be isolated from genomic DNA by nested PCR in a manner that does not lead to the amplification of the highly sequence related histone H3 gene. We also demonstrated that PCR based walking can be subsequently used to isolate the rest of the CENP-A gene and adjacent gene sequences. These adjacent gene sequences provide us with a primer binding sites for PCR isolation of the CENP-A gene from other percid species of fishes. An initial comparison of three percid species shows that the N-terminal tail of the percid CENP-A gene shows adaptive evolution.