To elucidate the mechanism of transcription and replication of Sendai
virus, we developed an efficient and faithful in vitro transcription s
ystem using purified virus particles. The in vitro RNA synthesis was a
lmost entirely dependent on the addition of eukaryotic cell extracts,
including those from various cultured mammalian cells, mammalian tissu
es, and even from plant cells. The RNA products were almost identical
to authentic mRNA species synthesized in the infected cells, in their
size distribution, the presence of 3'-poly(A) tail and the presence of
methylated 5'-cap structure (m(7)GpppAm). Ribonuclease protection exp
eriments after annealing the in vitro RNA with viral genomic RNA (vRNA
) indicated that the virion-associated RNA-dependent RNA polymerase tr
anscribes correct regions of the RNA genome in vitro. The active compo
nent(s) that is required for Sendai virus mRNA synthesis was partially
purified from bovine brain and was separated into at least two comple
mentary fractions, one of which could be replaced by highly purified c
ellular tubulin. When viral ribonucleoprotein complexes were used inst
ead of virus particles in the in, vitro transcription, only Sendai vir
us-infected cell extracts supported mRNA synthesis, and extracts from
uninfected cells or cells infected with other viruses were found to be
inert. These results suggest that, in addition to the general factors
which are present ubiquitously in eukaryotic cells, a factor(s) speci
fic to Sendai virus-infection is required for Sendai virus transcripti
on.