Further characterization of mRNA's of mouse hepatitis virus: presence of common 5'-end nucleotides

Abstract

The mouse hepatitis virus strain A59 codes for seven RNA species in the infected cells. These virus-specific RNAs were found to be polysome associated and therefore likely to represent mRNA's. All of them have common 3'-end sequences (Lai et al., J. Virol. 39:823-834, 1981). Their structure was further studied with respect to their 5'-end sequences. It was found that all of these mRNA's contained cap structures at their 5' ends. Furthermore, the capcontaining oligonucleotides which represent the sequences immediately adjacent to the 5' ends were found to be the same for most, if not all, of the seven virusspecific mRNA's. These sequences are also identical to the 5'-end sequences of the virion RNA genome. The 5'-end sequences were tentatively determined to be 5'-cap-N-UAAG. The presence of the common nucleotides in all of the virusspecific RNAs in mouse hepatitis virus strain A59 suggests several possible mechanisms of synthesis for these RNAs. The significance of these findings is discussed. Mouse hepatitis virus (MHV) is a member of Coronaviridae and contains a positive singlestranded 60S RNA _enome with a molecular weight of 5.4 x 10 (5). This RNA contains polyadenylic acid sequences at the 3' end (5, 16, 18) and a "cap" structure at the 5' end (6). It codes for at least three structural proteins, gp 90/ 180, pp 60, and gp 23 (12, 14), and probably three nonstructural proteins (1, 2, 10). The mode of synthesis of the viral RNA is still not clear. Recently, several laboratories have shown that seven virus-specific RNAs could be detected in the cells infected with MHV (4, 6a, 11; H. Wege, S. Siddell, M. Sturm, and V. ter Meulen, in V. ter Meulen, S. Siddell, and H. Wege, ed., Biochemistry and Biology of Coronaviruses, in press). These RNAs include the genomic RNA and six subgenomic RNA species. All of them contain polyadenylic acid sequences, suggesting that they represent mRNA's. By oligonucleotide mapping of these RNAs, we have further shown that the sequences of each virus-specific RNA are included within the next-larger RNA spe

Group 2 coronaviruses prevent immediate early interferon induction by protection of viral RNA from host cell recognition

“…dsRNA without 5′-triphosphates like poly (I:C), picornavirus RNA which contains VPg at the 5′-end or capped RNAs do not trigger IFN responses through RIG-I, but utilize MDA-5 . Coronavirus RNA is capped during replication by which RIG-I induction could be prevented (Lai et al, 1982). Since viral RNA synthesis occurs in the cytoplasm and host cell RNA modifications such as capping occur in the nucleus, many viruses have devised strategies to provide their own RNA modification machinery.…”

Characterization of the guanine-N7 methyltransferase activity of coronavirus nsp14 on nucleotide GTP

“…Finally, the GpppN cap is methylated by S-adenosyl-l-methionine (AdoMet or SAM)-dependent RNA (guanine-N7) methyltransferase (N7-MTase) at position 7 of the terminal guanosine. Although the final cap structures of viral and cellular mRNAs are very similar, RNA viruses have evolved diversified mechanisms to cap their mRNAs that are thus translated in the manner of eukaryotic mRNAs (Lai et al, 1982;Martin et al, 1975;Sagripanti et al, 1986;Shuman et al, 1980). For example, vaccinia virus employs a canonical pathway for mRNA capping, and the cap-0 structure at the 5 -end of vaccinia virus mRNA is formed by D1 (containing RNA TPase and GTase) and D12 (N7-MTase) by a mechanism analogous to the nuclear functions.…”

Primary structure and translation of a defective interfering rna of murine coronavirus

“…These mRNAs are arranged in the form of a 3' coterminal "nested" set, i.e., the sequence of each mRNA is contained entirely within the next larger mRNA (Lai et a/., 198 1;Leibowitz et al, 1981). In addition, each mRNA has a common leader sequence, which is derived from the 5' end of the genome (Lai et a/., 1982a(Lai et a/., , 1983Spaan et al, 1983). Several pieces of evidence demonstrated that MHV utilizes a novel mechanism of leader RNA-primed transcription, in which a free leader RNA species derived from the 5' end of genomic RNA is utilized as a primer for the transcription of subgenomic mRNAs (Baric eta/., 1983(Baric eta/., , 1985Makino et a/., 1986b).…”