Evolution of viral DNA-dependent RNA polymerases

Area of Science:

• Molecular Biology
• Virology
• Evolutionary Biology

Background:

• DNA-dependent RNA polymerase (DdRP) is crucial for transcription in prokaryotes, eukaryotes, and viruses.
• DdRPs are complex, multisubunit enzymes, with the largest subunit (RPO1) containing conserved motifs.
• Viral RPO1 sequences exhibit variations compared to their cellular counterparts.

Purpose of the Study:

• To identify and characterize the genes encoding the largest subunit of DdRP (RPO1) in insect iridescent virus type 6 (IIV6), fish lymphocystis disease virus (LCDV), and molluscum contagiosum virus (MCV-1).
• To compare the amino acid sequences and phylogenetic relationships of viral RPO1 with prokaryotic, eukaryotic, and other viral polymerases.
• To investigate the evolutionary origins of viral RPO1.

Main Methods:

• Polymerase Chain Reaction (PCR) technology was used to identify viral RPO1 genes.
• Extensive sequence analysis and comparison of amino acid sequences of RPO1 from various organisms.
• Phylogenetic tree construction using multiple amino acid alignments to infer evolutionary relationships.

Main Results:

• Viral RPO1 proteins possess conserved motifs (NADFDGD, RQP(TS)LH) but lack certain features found in eukaryotic RNAPII (e.g., C-terminal repetitive heptapeptide, specific amino acid in domain F).
• IIV6 and LCDV RPO1 show significant similarity to eukaryotic RNA polymerases, suggesting a closer evolutionary link to cellular enzymes.
• MCV-1 RPO1 exhibits higher homology to other viral RPO1s (e.g., vaccinia, variola virus), indicating a different evolutionary trajectory.

Conclusions:

• Viral RPO1 sequences display unique characteristics differentiating them from cellular polymerases.
• The RPO1 of IIV6 and LCDV likely evolved from eukaryotic RNAPII, while MCV-1 and related viruses may have diverged earlier.
• Comparative analysis of viral RPO1 provides insights into the diverse evolutionary pathways of viral transcription machinery.