Potential evolutionary influences on overlapping reading frames in the bovine leukemia virus pXBL region.
Bovine leukemia virus contains a pXBL region encoding the 3' parts of four regulatory proteins (Tax, Rex, G4, R3) in overlapping reading frames. Here we report the pXBL polymorphisms of 30 isolates from four countries. Rates of overall and synonymous substitutions were consistently lower, and nucleotide/amino acid composition bias and codon bias higher, in more-overlapped than in less-overlapped regions. Ratios of nonsynonymous/synonymous substitutions were lowest in the tax gene and its subregions. The 5' parts of the four genes showed selection patterns corresponding to their genomic context outside of the pXBL region. Longer G4 variants due to a natural stop codon mutation had additional triple overlap with reduced sequence variability. These data support the concept that a higher level of overlapping in coding regions correlates with greater evolutionary constraint. Tax, the most conserved among the four regulatory proteins, showed purifying selection consistent with its importance in the viral life cycle.
Zhao
Xiangrong
X
Graduate Program in Endocrinology, University of California at Berkeley, 3060 Valley Life Science Building, Berkeley, CA 94720-3140, USA. xzhao@berkeley.edu
McGirr
Kathleen M
KM
Buehring
Gertrude C
GC
D019143:Evolution, Molecular; D016370:Gene Products, rex / Q000235:genetics; D005807:Genes, Overlapping; D005814:Genes, Viral; D016355:Genes, pX; D001909:Leukemia Virus, Bovine / Q000235:genetics*; D008969:Molecular Sequence Data; D009856:Oncogene Proteins, Viral / Q000235:genetics; D011110:Polymorphism, Genetic; D016364:Reading Frames / Q000235:genetics*; D012641:Selection, Genetic
D016370:Gene Products, rex; D009856:Oncogene Proteins, Viral; C446341:g4 protein, Bovine leukemia virus