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Molecular studies of enzymes encoded by Chlorella viruses
Abstract
Chlorella viruses are large, icosahedral, dsDNA-containing viruses that infect certain unicellular, eukaryotic, chlorella-like green algae. Forty-two Chlorella NC64A viruses isolated from freshwater around the world encode a pyrimidine dimer-specific glycosylase, endonuclease enzyme (PDG), that initiates repair of UV-induced thymidine dimers. These PDG enzymes have 90 to 100% amino acid identity with the prototype chlorella virus PBCV-1 PDG. The pdg gene from 15 of these 42 viruses contained a 98-nucleotide intron and another 4 viruses contained a 81-nucleotide intron in the same position. The 19 introns in the pdg gene have the border sequences characteristic of a nuclear located spliceosomal processed intron. The DNA sequences of these introns were more conserved than those of their coding regions (exons). The ability of the viruses to repair DNA in the dark after UV exposure was indistinguishable among the intron-containing viruses and the intron-minus viruses. Virus PBCV-1 also encodes chitinases and chitosanase. Chitinase ORFs A181R and A182R became anew single ORF, A181/182R, after two sequence errors made previously were corrected. Therefore, the chlorella virus PBCV-1 genome contains two putative chitinase genes (a181/182r and a260r) and one putative chitosanase gene ( a292l). These three genes were cloned into expression vectors and expressed in Escherichia coli. The products of the chitinase and chitosanase genes in E. coli had the expected enzyme activity. Transcripts of a181/182r, a260r, and a292l genes were initially detected beginning at 30, 60, and 60 minutes, respectively, after virus infection and continuing until cells lysed. Proteins encoded by these genes were also detected in virus infected cell extracts beginning at 30, 90, and 240 minutes, respectively, post infection (p.i.). Homologs of the PBCV-1 chitinase and chitosanase genes were widespread among the chlorella viruses.
Subject Area
Molecular biology|Plant pathology|Genetics|Microbiology
Recommended Citation
Sun, Liangwu, "Molecular studies of enzymes encoded by Chlorella viruses" (1998). ETD collection for University of Nebraska-Lincoln. AAI9917862.
https://digitalcommons.unl.edu/dissertations/AAI9917862