MHV subgenomic negative strand function.

Abstract

Mouse hepatitis virus (MHV), a member of Nidovirales, contains a -32 KB linear, single-stranded, positive polarity RNA genome. Upon entry into the cell, the viral genome is transcribed into 7-8 subgenomic mRNAs ranging in size from ∼1.0-32.0 KB. The positive strand mRNAs are arranged in a 3′ co-terminal nested set, and each contains a 5’ end ∼72 nucleotide (nt) leader RNA sequence which is derived from the 5′ end of the genome. Leader RNA sequences are joined to body sequences of each subgenomic length mRNA at highly conserved transcriptional start (TSE) sites located just upstream from the coding sequences of each viral gene (Baric et al., 1983; Sethna et al, 1989). In addition to the viral mRNAs, both full-length as well as subgenomic length negative strand RNAs and replicative form (RF) RNAs have been detected in porcine transmissible gastro-enteritis virus (TGEV), bovine Coronavirus (BCV) and MHV-infected cells (Baric et al., 1983, Sethna et al., 1989; 1991; Sawicki and Sawicki, 1990). The subgenomic length negative strand RNA contains antileader RNA sequences (Sethna et al., 1991). It has been suggested that the subgenomic length negative strands function as dead end products of transcription (Yokomori et al., 1992; Jeong and Makino, 1992). In this manuscript, we provide direct evidence that the subgenomic negative strands function as the principle templates for the synthesis of each corresponding mRNA.