Aminoacylation of tRNAs encoded by Chlorella virus CVK2

Viruses that infect certain strains of the unicellular green alga, Chlorell a, have a large, linear dsDNA genome that is 330-380 kb in size; this genom ic size is the largest known among viruses:and is equivalent to similar to 60% of the smallest prokaryotic genome of Mycoplasma genitalium (580 kb). B esides many putative protein-coding genes a cluster of 10-15 tRNA genes is present in these viral genomes. Some of these tRNA genes contain peculiar i nsertions. In infected host cells, the viral tRNAs of CVK2, a Chlorella vir us isolate, have been demonstrated to be cotranscribed as a large precursor , similar to 1.0 kb in size, that is precisely processed into individual ma ture tRNA species. Acidic Northern blot analysis of eight of these tRNAs ha s revealed that they are actually aminoacylated in vivo, indicating their i nvolvement in viral protein synthesis. They may help the Virus reach maxima l replication potential by overcoming codon usage barriers that exist betwe en the virus and its host These results provide evidence that some componen ts of the host protein synthesis machinery can be replaced by viral gene pr oducts. This is the first report of tRNA aminoacylation encoded by viruses of eukaryotes. (C) 1999 Academic Press.