Intron conservation in the DNA polymerase gene encoded by Chlorella viruses

Area of Science:

• Virology
• Molecular Evolution
• Genomics

Background:

• Previous research identified spliceosomal introns in the pyrimidine dimer-specific glycosylase/apyrimidine lyase (pdg) gene of Chlorella NC64A viruses.
• Intron sequences in the pdg gene were found to be more conserved than their flanking exon regions.

Purpose of the Study:

• To investigate intron characteristics in the DNA polymerase (dnapol) gene of Chlorella NC64A and Pbi viruses.
• To compare intron conservation and phylogenetic relationships between pdg and dnapol genes in these viruses.

Main Methods:

• DNA sequencing of the dnapol gene and its flanking regions from 42 NC64A viruses and 5 Pbi viruses.
• Phylogenetic analysis to determine evolutionary relationships and ancestral intron states.
• Comparative sequence analysis of introns and exons.

Main Results:

• 38 of 42 NC64A viruses contained a 101-nucleotide intron in the dnapol gene; 4 contained an 86-nucleotide intron.
• The 4 viruses with the smaller dnapol intron also had smaller pdg introns.
• No dnapol introns were found in Pbi viruses; dnapol introns were phase 0 and highly conserved, similar to coding regions.

Conclusions:

• The 86-nucleotide dnapol intron is likely the ancestral form in NC64A viruses.
• Intron conservation in the dnapol gene is comparable to coding regions, contrasting with the pdg gene.
• Intron presence and size variation provide insights into viral evolution in Chlorella.