Abstract
This study of flavivirus genomes was facilitated by the amplification method developed in the thesis. The envelope (E) gene and non-structural protein five (NS5) were analysed for the existence of homologous nucleotide sequences in thirteen flaviviruses by reverse transcription/polymerase chain reaction from virus infected-cell RNA extracts. A homologous fragment of the NS5 gene was amplified from all the extracts. Subsequently homologous fragments from eighteen flavivirus infected-cell extracts, representative of every group of flaviviruses, were produced. The nucleotide sequences of the fragments were determined from a tick-borne virus, a mosquito-borne virus and a non-vector-borne virus. Two of these viruses (Banzi and Modoc) are classified into serocomplexes from which no viral genome sequence has previously been reported. The NS5 gene sequence of Banzi (BAN) virus and 90% of the gene sequence of Modoc (MOD) virus was subsequently determined. Comparison of the deduced amino-acid sequences with those of other reported flavivirus sequences confirmed the existence of functionally conserved motifs, which may be involved in RNA polymerase activities of the NS5 protein. A method of classification of flaviviruses on the basis of phylogenetic analysis of NS5 gene sequence was examined. The relationships between central european encephalitis (CEE), BAN, MOD and other flaviviruses were confirmed to be similar to those obtained from serological studies. Other nucleotide sequences determined, from regions flanking the NS5 gene showed the NS4B genes and 3' NC regions of BAN virus and yellow fever (YF) virus were highly similar. While the 3' NC region of MOD virus is not similar to that of any flavivirus previously sequenced.