Intron Conservation in a UV-Specific DNA Repair Gene Encoded by Chlorella Viruses |
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Authors: | Liangwu Sun Yu Li Amanda K McCullough Thomas G Wood R Stephen Lloyd Byron Adams James R Gurnon James L Van Etten |
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Institution: | (1) Department of Plant Pathology, University of Nebraska-Lincoln, NE 68583-0722, USA, US;(2) Sealy Center for Molecular Science, Department of Human Biological Chemistry and Genetics, The University of Texas Medical Branch, Galveston, TX 7555-1071, USA, US |
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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 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.
Received: 13 May 1999 / Accepted: 20 August 1999 |
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Keywords: | : Pyrimidine dimer-specific glycosylase — DNA repair — Intron — dsDNA virus — Chlorella viruses — Phycodnaviridae |
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