Molecular Biology of Fish Lymphocystis Disease Virus

Abstract

The fish lymphocystis disease virus (FLDV) can be classified genetically into two different strains: FLDV strain 1 (FLDV-f) occurs in flounders and plaice, whereas strain 2 (FLDV-d) is usually found in lesions of dabs. The genome structure of FLDV was found to be circularly permuted and terminally redundant combined with a high degree of methylation at CpG sequences. A defined and complete gene library of the FLDV genomes was established. The physical maps of the viral genomes were constructed for the restriction endonucleases BamHI, BstEII, EcoRI, and PstI. Two repetitive DNA elements were identified at the genome coordinates 0.034 to 0.052 (1413 bp) and 0.718 to 0.736 (1413 bp) of FLDV-f. The degree of DNA nucleotide homology between both regions was found to be 99%. The analysis of the DNA nucleotide sequence of the repetition in the genome of FLDV-d (1410 bp; EcoRI DNA fragment J) indicates that these repetitive DNA elements are highly conserved (94% homology). The DNA sequences of each strand of the individual repetitive element possess one open reading frame (150 to 339 amino acid residues). FLDV virions contain at least 33 polypeptides ranging in molecular weight from 220 to 14 Kd. A nucleoside triphosphate phosphohydrolase activity was found to be associated with FLDV. The thymidine kinase gene of FLDV-f has been identified at the genome coordinates 0.669 to 0.718 of the viral map units.