We studied the accumulation kinetics of murine coronavirus mouse hepat
itis virus (MHV) RNAs early in infection by using cloned MHV defective
interfering (DI) RNA that contained an intergenic sequence from which
subgenomic DI RNA is synthesized in MHV-infected cells. Genomic DI RN
A and subgenomic DI RNA accumulated at a constant ratio from 3 to 11 h
postinfection (p.i,) in the cells infected with MHV-containing DI par
ticles. Earlier, at 1 h p,i,, this ratio was not constant; only genomi
c DI RNA accumulated, indicating that MHV RNA replication, but not MHV
RNA transcription, was active during the first hour of MHV infection.
Negative-strand genomic DI RNA and negative-strand subgenomic DI RNA
were first detectable at 1 and 3 h p.i,, respectively, and the amounts
of both RNAs increased gradually until 6 h p,i, These data showed tha
t at 2 h p,i,, subgenomic DI RNA was undergoing synthesis in the cells
in which negative-strand subgenomic DI RNA was undetectable. These da
ta, therefore, signify that negative-strand genomic DI RNA, but not ne
gative-strand subgenomic DI RNA, was an active template for subgenomic
DI RNA synthesis early in infection.