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J. Virol., 03 1995, 1637-1644, Vol 69, No. 3
X Zhang and MM Lai
Previous studies suggested that coronavirus RNA transcription involves
interaction between leader RNA and the intergenic (IG) sequences, probably
via protein-RNA interactions (X. M. Zhang, C.-L. Liao, and M. M. C. Lai, J.
Virol., 68:4738-4746, 1994; X. M. Zhang and M. M. C. Lai, J. Virol.,
68:6626-6633, 1994). To determine whether cellular proteins are involved in
this process, we performed UV cross-linking experiments using cytoplasmic
extracts of uninfected cells and the IG (promoter) sequence between genes 6
and 7 (IG7) and the 5' untranslational region of mouse hepatitis virus
genomic RNA. We demonstrated that three different cellular proteins (p70,
p48, and p35/38) bound to the promoter sequence of the template RNA.
Deletion analyses of the template RNA mapped the binding site of p35/38 at
the consensus transcription initiation signal. In contrast, the binding of
p70 and p48 was less specific. p35/38 is the same protein as the one
previously identified to bind to the complementary strand of the leader
RNA; its binding affinity to the leader was approximately 15 times stronger
than that to IG7. Site-directed mutagenesis of the IG sequence revealed
that mutations in the consensus sequence of IG7 (UCUAAUCUAAAC to UCGAAAC
and GCUAAAG), which resulted in reduced subgenomic mRNA transcription, also
caused correspondingly reduced levels of p35/38 binding. These results
demonstrated that the extent of protein binding to the IG sequences
correlated with the amounts of subgenomic mRNAs transcribed from the IG
site. These studies suggest that these RNA-binding proteins are involved in
coronavirus RNA transcription and may represent transcription factors.
Copyright © 1995, American Society for Microbiology
Interactions between the cytoplasmic proteins and the intergenic (promoter) sequence of mouse hepatitis virus RNA: correlation with the amounts of subgenomic mRNA transcribed
Howard Hughes Medical Institute, University of Southern California School of Medicine, Los Angeles 90033-1054.
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