Abstract
All structural protein genes as well as one of the nonstructual protein NS1 gene of four dengue virus serotype 4 (DEN 4) strains recently isolated from patients admitted to the Children's Hospital in Bangkok, Thailand in 1993, were sequenced and analyzed. Isolates from a dengue fever (DF) case, CT93-77, dengue hemorrhagic fever (DHF) grade I cases, CT93-129 and CT93-158 as well as DHF grade II case, CT93-74 were selected in this study. It was found that the DHF grade II isolate had the highest percentage sequence divergence in the PrM and M regions from the published prototype strain (Caribbean, 814669). In all four Thai isolates, the C region had the lowest divergence, while the PrM region had the highest divergence both in nucleotide and amino acid sequence. In the whole analyzed regions, the percentage divergence ranges from 8.02-8.33% (nucleotide) and 3.97-4.90% (amino acid) respectively. Three amino acid replacements were found to be specific to the DF strain : at position 136, phenylalanine (F) instead of leucine (L); at position 914, phenylalanine (F) instead of serine (S) and at position 1, 042, glutamine (Q) instead of histidine (H). The mean hydrophobicity and isoelectric point value did not show significant differences in the sequenced region for all analyzed isolates. When compare to other strains from different geographical locations, four amino acid replacements were found unique to the Thai isolates. These were at position 269, isoleucine (I) instead of valine (V); at position 374, methionine (M) instead of valine (V); at position 482, threonine (T) instead of lysine (K) and position 608, threonine (T) instead of alanine (A). Phylogenetic analysis using the M/E junction showed that DEN 4 from different geographical areas can be classsified into three genotypic groups, and the Thai isolates were divided into two genotypes.
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