Abstract
BackgroundThe 5S ribosomal DNA (5S rDNA) is organized in tandem arrays with repeat units that consist of a transcribing region (5S) and a variable nontranscribed spacer (NTS), in higher eukaryotes. Until recently the 5S rDNA was thought to be subject to concerted evolution, however, in several taxa, sequence divergence levels between the 5S and the NTS were found higher than expected under this model. So, many studies have shown that birth-and-death processes and selection can drive the evolution of 5S rDNA. In analyses of 5S rDNA evolution is found several 5S rDNA types in the genome, with low levels of nucleotide variation in the 5S and a spacer region highly divergent. Molecular organization and nucleotide sequence of the 5S ribosomal DNA multigene family (5S rDNA) were investigated in three Pollicipes species in an evolutionary context.ResultsThe nucleotide sequence variation revealed that several 5S rDNA variants occur in Pollicipes genomes. They are clustered in up to seven different types based on differences in their nontranscribed spacers (NTS). Five different units of 5S rDNA were characterized in P. pollicipes and two different units in P. elegans and P. polymerus. Analysis of these sequences showed that identical types were shared among species and that two pseudogenes were present. We predicted the secondary structure and characterized the upstream and downstream conserved elements. Phylogenetic analysis showed an among-species clustering pattern of 5S rDNA types.ConclusionsThese results suggest that the evolution of Pollicipes 5S rDNA is driven by birth-and-death processes with strong purifying selection.
Highlights
The 5S ribosomal DNA (5S rDNA) is organized in tandem arrays with repeat units that consist of a transcribing region (5S) and a variable nontranscribed spacer (NTS), in higher eukaryotes
Nucleotide sequence analysis of 5S rDNA A total of 116 5S rDNA sequences from the genomes of P. pollicipes, P. elegans and P. polymerus was obtained experimentally to study the molecular evolution of 5S rDNA
We found up to seven different types of 5S rDNA based on the analysis of the NTS region
Summary
The 5S ribosomal DNA (5S rDNA) is organized in tandem arrays with repeat units that consist of a transcribing region (5S) and a variable nontranscribed spacer (NTS), in higher eukaryotes. The evolution of 5S rDNA units has classically been explained by the concerted evolution model, which suggests that molecular mechanisms such as gene conversion and unequal crossing-over play an important role in the homogenization of repeated units. These mechanisms maintain a high sequence similarity between copies and prevent the independent evolution of each member of a multigenic family [4]. Under the birth-and-death evolution model, new variants are created by gene duplication and can remain as functional genes in the genome or become pseudogenes In this way, transcribing region conservation could be explained by purifying selection, as suggested by Nei and Rooney [10]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
