Characterization of viruses infecting a eukaryotic Chlorella-like green alga

Schuster, Anne; Burbank, Dwight E.; Meister, Barbara; Skrdla, Merri P.; Meints, Russel H.; Hattman, Stanley; Swinton, David; Etten, James L. Van

doi:10.1016/0042-6822(86)90276-x

Cited by 51 publications

(40 citation statements)

References 18 publications

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“…The burst size of the MT325 virus is similar to that of PBCV-1, so this virus compensates for the lack of host DNA degradation by some other mechanism. (ii) Host DNA degradation may contribute to the rapid inhibition of host-directed DNA and RNA syntheses that occurs in PBCV-1-infected chlorella cells (19,24). Inhibiting host RNA synthesis is important because the chloroviruses do not carry a recognizable RNA polymerase, nor is RNA polymerase activity associated with the virion (22).…”

Section: Discussionmentioning

confidence: 99%

Virion-Associated Restriction Endonucleases of Chloroviruses

Agarkova

Dunigan

Etten

2006

J Virol

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Chloroviruses are large, double-stranded-DNA, plaque-forming viruses that infect certain eukaryotic chlorella-like green algae. The prototype of the genus is Paramecium bursaria chlorella virus 1 (PBCV-1). Chlorovirus genomes contain various amounts of methylated nucleotides due to virus-encoded DNA methyltransferases (MTases); about 25% of the MTases are associated with companion DNA site-specific (restriction) endonucleases (REases). These enzymes constitute virally encoded restriction-modification (R/M) systems. Although several of the chlorovirus R/M systems are characterized, their biological functions are unknown. The PBCV-1 proteome reveals that two virus-encoded REases, but not their companion MTases, are virion associated, suggesting that viral REases might help degrade the host DNA early in infection. To test this hypothesis, host chromosomal DNA from PBCV-1-infected cells was examined by pulsed-field gel electrophoresis. Initiation of host chromosomal DNA degradation occurred within 5 min postinfection (p.i.). The DNA degradation was insensitive to protein synthesis inhibitors or UV inactivation of virus particles, consistent with the agent being a small protein associated with the virion. Nuclease activities, including those of the two predicted REases and an uncharacterized general nuclease(s), were detected in disrupted PBCV-1 particles. The general nuclease(s) degraded both host and viral DNAs in vitro, although the viral DNA was not degraded in vivo, suggesting differential intracellular trafficking of the virion-associated nucleases. Infection with chloroviruses lacking an R/M system(s) resulted in either delayed host chromosomal DNA degradation or no detectable host chromatin changes. These immediate-early events associated with chlorovirus infections may facilitate rapid switching of the host transcriptional apparatus to viral transcription, which begins within 5 to 10 min p.i.Chloroviruses are large, icosahedral, plaque-forming, genetically diverse but morphologically similar, linear, doublestranded-DNA (dsDNA) viruses (315 to 380 kb) that belong to the family Phycodnaviridae and the genus Chlorovirus (8, 22). The prototype chlorovirus, Paramecium bursaria chlorella virus 1 (PBCV-1), has a 331-kb genome that contains 366 proteinencoding genes and a polycistronic tRNA gene encoding 11 tRNAs. The chloroviruses infect certain freshwater, unicellular, chlorella-like green algae (e.g., Chlorella strain NC64A or Chlorella strain Pbi), which normally exist as endosymbionts in the protozoan Paramecium bursaria. Viruses that infect Chlorella NC64A (NC64A viruses) are serologically different from viruses that infect Chlorella Pbi (Pbi viruses). NC64A viruses neither infect nor attach to Chlorella Pbi, and vice versa (16).One distinctive feature of the chloroviruses is that their genomes contain methylated nucleotides: 5-methylcytosine (m5C) levels range from 0.1% to 47% of the total cytosines, and N 6 -methyladenine (m6A) levels vary from 0% to 37% of the total adenines (25, 26). The discovery that m5C...

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Section: Discussionmentioning

confidence: 99%

Virion-Associated Restriction Endonucleases of Chloroviruses

Agarkova

Dunigan

Etten

2006

J Virol

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“…Twenty-nine of the 42 viruses used in this study were isolated from water samples collected in different regions of the United States in 1983-1984(Van Etten et al 1985aSchuster et al 1986) and seven were isolated from water collected in China in 1987 (Zhang et al 1988). Including PBCV-1, which was isolated in 1981, several criteria were used to group these 37 viruses into 16 classes (Table 1) (Van Etten et al 1991).…”

Section: The Pdg Gene Is Widespread In the Chlorella Virusesmentioning

confidence: 99%

“…Large (150 to 190 nm in diameter) icosahedral, plaqueforming, dsDNA-containing viruses that infect certain isolates of unicellular, eukaryotic chlorella-like green algae are common in freshwater collected throughout the world (Van Etten et al 1985a, b;Schuster et al 1986;Zhang et al 1988;Yamada et al 1991). Virions of the prototype chlorella virus, PBCV-1, contain at least 50 proteins and a lipid component located inside the outer glycoprotein capsid (Skrdla et al 1984;Wang et al 1993).…”

Section: Introductionmentioning

confidence: 99%

Intron Conservation in a UV-Specific DNA Repair Gene Encoded by Chlorella Viruses

Sun

Liu²,

McCullough

et al. 2000

J Mol Evol

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Abstract. Large dsDNA-containing chlorella viruses encode a pyrimidine dimer-specific glycosylase (PDG) that initiates repair of UV-induced pyrimidine dimers. The PDG enzyme is a homologue of the bacteriophage T4-encoded endonuclease V. The pdg gene was cloned and sequenced from 42 chlorella viruses isolated over a 12-year period from diverse geographic regions. Surprisingly, the pdg gene from 15 of these 42 viruses contain a 98-nucleotide intron that is 100% conserved among the viruses and another 4 viruses contain an 81-nucleotide intron, in the same position, that is nearly 100% identical (one virus differed by one base). In contrast, the nucleotides in the pdg coding regions (exons) from the introncontaining viruses are 84 to 100% identical. The introns in the pdg gene have 5Ј-AG/GTATGT and 3Ј-TTGCAG/ AA splice site sequences which are characteristic of nuclear-located, spliceosomal processed pre-mRNA introns. The 100% identity of the 98-nucleotide intron sequence in the 15 viruses and the near-perfect identity of an 81-nucleotide intron sequence in another 4 viruses imply strong selective pressure to maintain the DNA sequence of the intron when it is in the pdg gene. However, the ability of intron-plus and intron-minus viruses to repair UV-damaged DNA in the dark was nearly identical. These findings contradict the widely accepted dogma that intron sequences are more variable than exon sequences.

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“…The growth of the host Chlorella strain NC64A on MBBM medium, the production of the viruses (listed in Table 1), and the procedures used to measure virus adsorption and virus growth have been described (Van Etten et al, 1983a, b;Schuster et al, 1986).…”

Section: Methodsmentioning

confidence: 99%

“…These viruses can be distinguished by differences in plaque size, antigenic specificity, DNA restriction fragment patterns and the nature and abundance of methylated bases in their genomic DNAs (Schuster et al, 1986). Each of the virus DNAs contains 5-methylcytosine (5mC); the concentration of 5mC varies from 0.1 ~ to 47"5~o of the total cytosine residues.…”

Section: Introductionmentioning

confidence: 99%