- Volume 68, Issue 12, 1987

Humoral antibody responses to Theiler’s murine encephalomyelitis virus (TMEV) capsid proteins were examined. Rabbit antisera produced against the native BeAn strain of TMEV and against the isolated capsid proteins (VP1, VP2 and VP3) were tested for their ability to bind or neutralize virus and to inhibit the virus-induced haemagglutination of human O+ erythrocytes. Western immunoblotting analysis showed that isolated VP1, VP2 and VP3 each primed for a specific antibody response, but that native virions primed for antibodies specific for VP1 and VP2, but not VP3. Virus neutralization studies revealed that a dominant TMEV neutralizing determinants) lay on VP1, as did the haemagglutinating determinant. The possible location of the neutralizing epitopes are discussed on the basis of molecular modelling of the predicted amino acid sequence of TMEV from that of the closely related Mengo virus for which the three-dimensional structure is known.

The viral capsid protein VP1 of human rhinovirus serotype 2 (HRV2) was cleaved with cyanogen bromide. The peptides thus obtained were separated on an HPLC butyl reversed phase column. Their positions on VP1 were determined by amino-terminal sequencing using the known nucleotide sequence of the genomic RNA of HRV2. The putative carboxy-terminal peptide was further cleaved with trypsin and the resulting fragments were separated on a C18 reversed phase column. Amino-terminal sequencing of the C-terminal peptide revealed alanine as being the carboxy terminus of VP1 in HRV2. This indicates that the processing of the polyprotein is different in HRY2 from the processing previously reported for HRV14 and poliovirus.

The capsid proteins of three potato virus X isolates that belong to different strain groups on the basis of their reactions with host resistance genes have been compared by means of SDS-PAGE and partial proteolysis mapping. Considerable differences were observed in both the migration rates in SDS-PAGE and the peptide patterns generated after partial digestion with V8 protease of the capsid proteins of the isolates. The high molecular weight proteins synthesized by in vitro translation of genomic RNAs extracted from the three isolates were electrophoretically indistinguishable and antigenically unrelated to capsid proteins.

Repeated selection of plants with unusually severe symptoms after their inoculation by insect vectors which had been injected with dilute inoculum from crude extracts of a stock culture (O strain) of rice dwarf virus (RDV) resulted in the emergence of a severe isolate (S strain). Of the 12 segments of RDV RNA, the fourth largest RNA of the S strain had an apparent M r about 20000 larger than that of the corresponding segment of the O strain. The M r of the protein corresponding to the M r 43000 protein of the O strain, which is located on the outside of the outer capsid, was 44000 in the S strain. The implication of the differences in the RNA and protein components between the S and O strains is discussed.

The expression of cauliflower mosaic virus proteins was examined in crown gall tissue transformed by integration of virus genome DNA into plant host chromosomes by Agrobacterium tumefaciens-mediated transfer. Galls upon plants of species that support infection by virus particles as well as upon non-host plants were analysed by immunoblotting using antisera specific to proteins encoded by viral genes I, IV and VI. The product of viral gene VI was present in all plants tested, but no other viral gene products could be detected in any host.