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Chlorella virus PBCV-1 encodes a functional homospermidine synthase.
A Kaiser1, M Vollmert, D Tholl
1Institut fur Pharmazeutische Biologie, Technische Universitaet Braunschweig, Mendelssohnstrasse 1, Braunschweig, Germany.
Virology
|November 2, 1999
Summary
This study identifies a novel virus-encoded enzyme, homospermidine synthase, involved in polyamine biosynthesis. This discovery is significant as it
Area of Science:
- Virology
- Molecular Biology
- Biochemistry
Background:
- Chlorella viruses possess large double-stranded DNA genomes.
- Polyamines are essential for cellular processes, including DNA stabilization.
- The biosynthesis pathways of polyamines in viruses are largely uncharacterized.
Purpose of the Study:
- To investigate the function of the PBCV-1 A237R gene.
- To determine if PBCV-1 encodes enzymes involved in polyamine biosynthesis.
- To explore the presence and significance of homospermidine in PBCV-1.
Main Methods:
- Sequence analysis of the PBCV-1 genome to identify open reading frames.
- Gene expression and protein purification of the A237R product in Escherichia coli.
- Biochemical assays to characterize the enzymatic activity of the recombinant protein.
- Analysis of polyamine content in PBCV-1 infected and uninfected Chlorella, and in PBCV-1 virions.
Main Results:
- A novel open reading frame, A237R, was identified in the PBCV-1 genome, encoding a homospermidine synthase.
- The recombinant A237R protein catalyzes the NAD(+)-dependent synthesis of homospermidine from putrescine.
- Homospermidine was detected in PBCV-1 infected and uninfected Chlorella, and within PBCV-1 virions.
- The A237R gene is expressed late during PBCV-1 infection and is conserved across chlorella viruses.
Conclusions:
- PBCV-1 encodes a functional homospermidine synthase, representing the first known instance of a virus encoding a polyamine biosynthesis enzyme.
- The biological role of homospermidine in PBCV-1 remains unclear due to insufficient quantities for significant DNA neutralization.
- The widespread presence of the homospermidine synthase gene among chlorella viruses suggests an important, yet unknown, viral function.