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

The family Coronavirtdae comprises a monogeneric group of 11 viruses which infect vertebrates. The main characteristics of the member viruses are: (i) Morphological: Enveloped pleomorphic particles typically 100 nm in diameter (range 60–220 nm), bearing about 20 nm long club-shaped surface projections, (ii) Structural: A single-stranded infectious molecule of genomic RNA of about (5–7) × 10⁶ molecular weight. A phosphorylated nucleocapsid protein [mol.wt. (50–60) × 10³] complexed with the genome as a helical ribonucleoprotein; a surface (peplomer) protein, associated with one or two glycosylated polypeptides [mol.wt. (90–180) × 10³]; a transmembrane (matrix) protein, associated with one polypeptide which may be glycosylated to different degrees [mol.wt. (20–35) × 10³]. (iii) Replicative: Production in infected cells of multiple 3’ coterminal sub genomic mRNAs extending for different lengths in the 5’ direction. Virions bud intracytoplasmically. (iv) Antigenic: 3 major antigens, each corresponding to one class of virion protein, (v) Biological: Predominantly restricted to infection of natural vertebrate hosts by horizontal transmission via the fecal/oral route. Responsible mainly for respiratory and gastrointestinal disorders.

Enzymatic markers and electron microscopy were utilized to determine the cellular origin of the membrane types isolated from type 2 dengue virus-infected BHK cells by discontinouous sucrose gradient centrifugation. The results showed an apparent separation of plasma membrane, smooth and rough endoplasmic reticulum with increasing density. Virus-induced protein and RNA synthesis, as indicated by the incorporation of radiolabeled precursors, was localized on the rough endoplasmic reticulum. Glycosylation, measured by the incorporation of radiolabeled glucosamine into membrane-associated proteins, was most active in the bands of intermediate and smooth endoplasmic reticulum. Polyacrylamide gel electrophoresis of isolated membrane bands, radiolabeled in the presence of actinomycin D, after pulse inhibition by cycloheximide, revealed seven virusspecified proteins associated with all membrane fractions. Viral structural protein V-3, and nonstructural proteins NV-3 and NV-2, increased with decreasing density, whereas NV-5 and NV-4 remained constant. The viral capsid protein V-2 was depleted in the intermediate and smooth endoplasmic reticulum, suggesting that these membranes may serve as the sites for viral maturation. NV-3 was the most prominent virus-specified protein found in the plasma membrane.

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