A Highly Divergent Actin Gene in the Nuclear Genome of the Cryptophyte Alga Pyrellolllollns helogolandica
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The cryptophytes are a monophyletic group of unicellular algae with plastids bound by four membranes. One characteristic that all cryptophytes share is a structure between the second and third membranes called a nucleomorph. Believed to be the vestigial nucleus of an algal endosymbiont, the nucleomorph holds many clues to the process of secondary endosymbiosis. In this paper we examine two actin genes from a cryptophyte alga, Pyrenomonas helgolandica. While one actin is typical for the cryptophytes, the other is highly divergent and believed to have originated in the nucleomorph. We have completed the sequencing of these two genes and examined the differences between the two. By exploring the fate of a gene with origins in the nucleomorph, we hope to better understand secondary endosymbiosis, plastid evolution, and gene transfer. In addition to these issues, we also provide evidence for previously undescribed introns in the 5' end of the divergent actin.