Analysis of 138 kb of DNA sequences of the Chlorella virus PBCV-1 genome

One hundred and thirty-eight kb of DNA, including forty-five kb of DNA at the left terminus, forty-three kb of DNA at the right terminus and fifty kb of DNA located at map position 90-140 in the 330 kb Chlorella virus PBCV-1 genome were cloned, sequenced, and analyzed. Two hundred and seventy-four complete open reading frames (ORFs) larger than 195 nucleotides were identified. One hundred and forty-three of the 274 ORFs, which are densely packed on both strands of the DNA, were considered major ORFs and are likely to encode functional gene products. Thirty-eight major ORFs resemble one or more genes in the databases. The remaining 105 major ORFs are unique. Several expected genes were found in the PBCV-1 genome, including: a DNA polymerase, a large subunit of ribonucleotide diphosphate reductase, a proliferating cell nuclear antigen, protein kinases and a UV damage repair gene. These genes are probably essential for viral replication. In addition, several unexpecteded putative genes were also found, including: a fungal translation elongation factor 3 (EF-3), a nucleotide diphosphate sugar dehydrogenase, a Cu-Zn superoxide dismutase, an orthinine decarboxylase, a glycerophosphoryl diester phosphodiesterase, a D-hydroxyisocaproate dehydrogenase, a nitrilase, a restriction endonuclease and an adenine-specific DNA methyltransferase, a nonfunctional cytosine-specific DNA methyltransferase, at least three chitinases, three ORFs which could encode proteins homologous to the virus major capsid protein, and six ORFs containing ankyrin-like repeats. Some of the unexpected genes have never been found before in a virus genome. Understanding the role some of these gene products play in the viruses life cycle should provide important information on the unusual lifestyle of these viruses