Springer Online Journal Archives 1860-2000
Summary. Mutations in the fusion, F, protein of Sendai virus resulting in increased cleavability by ubiquitous host protease(s), and mutations in the matrix, M, protein resulting in bipolar budding, are both important determinants for the systemic infection in mice caused by the protease activating pantropic mutant, F1-R. Several mutants of Sendai virus (BY, BF, and KD-M) with phenotypes of bipolar budding and/or increased cleavability of F protein were isolated. Genomic RNA sequence analysis of the F and M genes of the mutants revealed that several deduced amino acids in the F and M proteins were different from those of F1-R, T-5 (a revertant of F1-R), and wild-type viruses. The BF and KD-M mutants that budded bipolarly and were also activated by ubiquitous proteases were examined for replication in tissue culture cells and in mice. All of the mutants exhibited multiple-step replication in MDCK, MDBK, and LLC-MK2 cells without trypsin, but formed plaques only in MDCK cells. One of the mutants, designated KD-52M, was similar to F1-R in that it formed plaques in all three cell lines without addition of exogenous protease. However, none of the mutant viruses, including KD-52M, caused a systemic infection in mice. The mutated M protein of F1-R enhances the disruption of microtubles. However, none of the mutants with a bipolar budding phenotype (BY, BF, and KD-M), disrupted the microtubules to the same extent as F1-R. All of these mutants had mutations in the M protein that were different from those found in F1-R. Taken together, these results suggest that mutations at Ser115 to Pro in the F protein and at Asp 128 to Gly and Ile210 to Thr in the M protein of F1-R are the mutations specifically required for the systemic infection caused by F1-R.
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