Search for: All records

Proliferating cell nuclear antigen (PCNA) plays critical roles in eukaryoticDNAreplication and replication‐associated processes. It is typically encoded by one or two gene copies (pcna) in eukaryotic genomes. Recently reported higher copy numbers ofpcnain some dinoflagellates raised a question of how this gene has uniquely evolved in this phylum. Through real‐timePCRquantification, we found a wide range ofpcnacopy number (2–287 copies) in 11 dinoflagellate species (n = 38), and a strong positive correlation betweenpcnacopy number and genome size (log₁₀–log₁₀transformed). Intraspecificpcnadiverged up to 21% and are dominated by nonsynonymous substitutions, indicating strong purifying selection pressure on and hence functional necessity of this gene. By surveyingpcnacopy numbers in eukaryotes, we observed a genome size threshold at 4 pgDNA, above which more than twopcnacopies are found. To examine whether retrotransposition is a mechanism ofpcnaduplication, we measured the copy number of retroposedpcna, taking advantage of the 22‐nt dinoflagellate‐specific spliced leader (DinoSL) capping the 5′ end of dinoflagellate nuclear‐encodedmRNAs, which would exist in the upstream region of a retroposed gene copy. We found that retroposedpcnacopy number increased with totalpcnacopy number and genome size. These results indicate co‐evolution of dinoflagellatepcnacopy number with genome size, and retroposition as a major mechanism ofpcnaduplication in dinoflagellates. Furthermore, we posit that the demand of faithful replication and maintenance of the large dinoflagellate genomes might have favored the preservation of the retroposedpcnaas functional genes.