CORONAVIRUS TRANSLATIONAL REGULATION - LEADER AFFECTS MESSENGER-RNA EFFICIENCY

Cells infected with the murine coronavirus, mouse hepatitis virus (MHV ), show decreased host protein synthesis concomitant with an increase in viral protein synthesis. We examined the in vitro translation prope rty of the conserved MHV 5'-leader RNA sequence by constructing chimer ic mRNAs in which the 72-nt 5'-leader of M protein mRNA (A59 strain) w as positioned upstream of the human alpha-globin coding region in a T7 expression vector. Synthetic 5'-capped transcripts of these mRNA cons tructs were translated in cell-free extracts prepared from uninfected and MHV-infected murine DBT cells. Nonviral mRNAs translated readily i n both uninfected and infected cell-free extracts. By contrast, replac ement of the human alpha-globin 5'-untranslated region (UR) with the M HV 5'-leader increased translation ca. three- to fourfold in cell-free extracts from MHV-infected cells versus translation in extracts from uninfected cells. Chimeric globin mRNA containing the reverse compleme ntary sequence of the viral leader RNA in the 5'-UR showed no such inc rease in translation, indicating sequence specificity for the effect. A 13-nt region (-UCUAAUCCAAACA-) immediately proximal to the start cod on was found to be important for the increased translation of the MHV leader-containing mRNAs. These data indicate that the apparent downreg ulation of host translation is not primarily due to an inhibition of h ost translation but also invokes a significant stimulation of viral tr anslation in cis by a structural feature of the MHV 5'-leader RNA sequ ence in conjunction with a virus-specified or virus-induced factor. (C ) 1994 Academic Press, Inc.