Exploring the Remote Ties between Helitron Transposases and Other Rolling-Circle Replication Proteins.

Area of Science:

• Genetics and Genomics
• Molecular Biology
• Evolutionary Biology

Background:

• Rolling-circle replication (RCR) elements, including viruses, plasmids, and transposons, are widespread across all life domains.
• Eukaryotic RCR transposons, known as Helitrons, are prevalent in eukaryotic genomes, sometimes constituting large fractions.
• The evolutionary relationships between Helitrons and other RCR elements remain largely unknown.

Purpose of the Study:

• To investigate the evolutionary origins of Helitrons by comparing their transposase sequences with RCR proteins from diverse mobile genetic elements.
• To elucidate the phylogenetic relationships among different RCR elements, including viruses, plasmids, and transposons.

Main Methods:

• Comparative analysis of endonuclease domain sequences from Helitron transposases and various RCR proteins.
• Application of stepwise alignment, phylogenetic analysis, and multidimensional scaling (MDS) for relationship mapping.

Main Results:

• Helitron transposases exhibit greater sequence similarity to proteins from prokaryotic viruses and plasmids than to prokaryotic transposons or eukaryotic viruses.
• Evidence supports the classification of RCR endonucleases into three distinct groups: Y1, Y2, and Yx.
• Prokaryotic mobile genetic elements are identified as the probable closest ancestors of eukaryotic Helitrons.

Conclusions:

• Eukaryotic Helitrons likely evolved from prokaryotic RCR elements, specifically viruses and plasmids.
• The study provides a refined classification of RCR endonucleases, highlighting evolutionary connections.
• Findings underscore the dynamic and interconnected nature of mobile genetic elements across different biological domains.