Intron conservation in a UV-specific DNA repair gene encoded by chlorella viruses

Liangwu Sun, Yu Li, Amanda K. McCullough, Thomas G. Wood, R. Stephen Lloyd, Byron Adams, James R. Gurnon, James L. Van Etten

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


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 intron-containing viruses are 84 to 100% identical. The introns in the pdg gene have 5'-AG/GTATGT and 3'- 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.

Original languageEnglish (US)
Pages (from-to)82-92
Number of pages11
JournalJournal of Molecular Evolution
Issue number1
StatePublished - 2000


  • Chlorella viruses
  • DNA repair
  • Intron
  • Phycodnaviridae
  • Pyrimidine dimer-specific glycosylase
  • dsDNA virus

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Molecular Biology
  • Genetics


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