Intron conservation in the DNA polymerase gene encoded by Chlorella viruses

Previously we reported that 19 of 42 viruses that infect Chlorella strain N C64A (NC64A viruses) contain a short, nuclear-located, spliceosomal-process ed intron in a pyrimidine dimer-specific glycosylase/apyrimidine lyase (pdg ) gene. Surprisingly, the nucleotide sequence of the intron region is more conserved than the exon regions of the gene (L. Sun et ah, 2000, J. Mol. Ev ol. 50, 82-92). For comparative purposes, we determined the nucleotide sequ ence of a similar intron type and its flanking coding regions in the DNA po lymerase (dnapol) gene from the same 42 NC64A viruses and also 5 viruses th at infect Chlorella Strain Pbi. Thirty-eight of the 42 NC64A viruses contai ned a 101-nucleotide intron and the remaining 4 had an 86-nucleotide intron located in the same position in dnapol. The 4 viruses with the smaller int ron in dnapol also have a smaller intron in their pdg gene. There was no in tron in the dnapol gene of the 5 Pbi viruses. Phylogenetic analyses indicat e that the dnapol genes containing the 86-nucleotide intron represent the a ncestral condition among the NC64A viruses. The intron in the dnapol gene i s phase 0 (keeps codons intact), which differs from the phase 1 intron in t he pdg gene. The intron in the dnapol gene, unlike the pdg intron, was cons erved (83 to 100% identical) to about the same extent as the coding regions of the gene (78 to 100% identical). (C) 2001 Academic Press.