ANALYSIS OF 74 KB OF DNA LOCATED AT THE RIGHT END OF THE 330-KB CHLORELLA VIRUS PBCV-1 GENOME

This report completes a preliminary analysis of the sequence of the 33 0,740-bp chlorella virus PBCV-1 genome, the largest virus genome to be sequenced to date. The PBCV-1 genome is 57% the size of the genome fr om the smallest self-replicating organism, Mycoplasma genitalium. Anal ysis of 74 kb of newly sequenced DNA, from the right terminus of the P BCV-1 genome, revealed 153 open reading frames (ORFs) of 65 codons or longer. Eighty-five of these ORFs, which are evenly distributed on bot h strands of the DNA, were considered major ORFs. Fifty-nine of the ma jor ORFs were separated by less than 100 bp. The largest intergenic di stance was 729 bp, which occurred between two ORFs located in the 2.2- kb inverted terminal repeal region of the PBCV-1 genome. Twenty-seven of the 85 major ORFs resemble proteins in databases, including the lar ge subunit of ribonucleotide diphosphate reductase, ATP-dependent DNA ligase, type II DNA topoisomerase, a helicase, histidine decarboxylase , dCMP deaminase, dUTP pyrophosphatase, proliferating cell nuclear ant igen, a transposase, fungal translation elongation factor 3 (EF-3), UD P glucose dehydrogenase, a protein kinase, and an adenine DNA methyltr ansferase and its corresponding DNA site-specific endonuclease. Sevent een of the 153 ORFs resembled other PBCV-1 ORFs, suggesting that they represent either gene duplications or gene families. (C) 1997 Academic Press.