| Research Abstract |
1) S segment of B-1 strain of HFRS virus was cloned and all of its nucleotide sequence was determined by the same method as used for M segment. When the deduced amino acid sequence was compared to that of SR-11, which included in the same serotype, Hantaan and Hallnas strains, 98.4%, 83.2% and 61.7% homologies were observed, respectively. The amino acid similarities indicate that B-1 strain evolved from Hantaan strain and SR-11 strain came from B-1 strain by flame sift. Moreover, it was shown that there were one of two sites where amino acid sequence change observed in the four serotypes commonly. When the amino acid sequence of L segment of B-1 strain was compared to that of Hantaan and Hallnas strains, 83.0% and 73.5% homologies were observed, respectively, indicating that the L segment has the highest conservation in the three segments of HFRS virus. In addition, the region predicted to encodeactive center of RNA dependent RNA polymerase was highly conserved. The L segment also demo
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nstrated to have sites where amino acid sequence change observed in the four serotypes commonly.
2) The Hantaan virus (HTN) of Hantavirus genus causes a fatal disease in suckling mice following intraperitoneal of intracerebral infection. HTN cl-1, which was obtained from the 76-118 strain of HTN by plaquing in Vero E6 cells, exhibited increased mortality rates in mice whereas mice infected with HTN cl-2 showed no clinical signs (Tamura et al., 1989). As a first step to understand the molecular basis for the marked difference in virulence, we compared the nucleotide sequences of the large (L), medium (M) and small (S) segments of HTN cl-1 genome with those of HTN cl-2 and found that there was only one substitution in position 1124 of the glycoprotein encoded by the M genome segment, in which serine of HTN cl-1 was replaced by glycine of HTN cl-2. Although there were several nucleotide and amino acid differences between the parental strain and HTN cl-1, the amino acid in position 1124 of the glycoprotein of the 76-118 strain was also the same serine as HTN cl-1, which was also pathogenic virus. These suggest that this substitution may be responsible for some of the virus characteristics related to virulence.
3) The rats infected with HFRS virus usually maintain the virus persistently and become virus carrier without showing viruses in the blood. However, in some rats RNA dependent RNA polymerase can be detected in the bone marrow and leukocytes. Therefore, in the present study, we tried to isolate virus genes of Hantaan type virus from a subject who had been infected with Hantavirus 49 years ago demonstrating high antibody titer without showing any virus antigens in the blood. As a results, virus genome of Hantaan type could be isolated, and thus indicate that the virus can be maintained for a long period even in human as genome. Less
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