Large deletions in the genome of Chlorella virus CVK1

Large (30-45 kbp) deletions were induced in the Chlorella virus CVK1 genome by UV irradiation. Restriction endonuclease maps of the mutant genomes showed that these deletions occurred in a region located from 1.5 kbp to 47 kbp from the left DNA end. The nucleotide sequences determined around the deletion boundaries indicate that the deletion process took place by both homologous and nonhomologous recombinations. In one case, the recombination site was within a region of about 600 bp, consisting of 40 tandem repetitions of a 15-bp sequence element. The deleted region may contain several multigene families. Northern blot analyses with probes including the genes for translational elongation factor 3 and DNA polymerase showed no discernible aberrancy in the gene expression patterns in the mutants. However, at least two protein bands were missing from the mutant virions.