Date of Award:

5-1989

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Joseph K. -K. Li

Committee

Joseph K. -K. Li

Committee

Neil Van Alfen

Committee

Jeffery K. Kondo

Committee

J. Y. Takemoto

Committee

Dennis Welker

Abstract

A study was undertaken to better understand the genetic relationship of five United States prototype bluetongue virus serotypes. Genomic double-stranded RNA segment S1, which encodes the major core protein and serogroup antigen, VP7, was used as a marker gene for the sequence analyses. The S1 segments from BTV-2, 11, 13, and 17 were cloned and sequenced by methods developed during the course of this investigation. These results were compared with previously published sequence data from segment S1 of BTV-10. The Sl segments are 1156 base pairs long and contain a common open reading frame capable of coding for a protein (VP7) of 349 amino acids. This reading frame is flanked by an 18 base 5' noncoding stretch and an 89 base 3' noncoding region. Both termini are well conserved among the serotypes. The 3' end of each serotype has the potential to form a stable stem-loop structure. VP7 is very well conserved among the five serotypes. It has a predicted charge of +1 to +1.5 at pH 7.0. Hydropathy and secondary structure predictions show an alternating pattern of hydrophobic and hydrophilic amino acid regions. Based on this data, an eight-stranded ß-barrel is predicted for VP7. Proteins of similar function in single-stranded RNA viruses have this same structure. This observation suggests a common origin of bluetongue viruses with single-stranded RNA viruses. The ß-barrel may also serve as a target for antiviral drugs as is the case with picornaviruses. Phylogenetic analyses show that BTV-2, 10, 11, and 17 are closely related and that BTV-13 is the most distant of the five United States serotypes. Similar comparisons of the previously published L2 sequence show a similar pattern. By using the 29-year span between the appearance of BTV-10 and BTV-2 in the United States, an evolutionary rate of 2.2 x 10-3 nucleotide substitutions/site/year was estimated. This is similar to the gag gene of retroviruses and the RNA polymerase gene of influenza. A rate of this magnitude is evidence that double-stranded RNA viruses, like single-stranded RNA viruses, do not have polymerase proofreading activity.

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