TGEV corona virus ORF4 encodes a membrane protein that is incorporated into virions

Abstract

The coding potential of the open reading frame ORF4 (82 amino acids) of transmissible gastroenteritis virus (TGEV) has been confirmed by expression using a baculovirus vector. Five monoclonal antibodies (MAbs) raised against the 10K recombinant product immunoprecipitated a polypeptide of a similar size in TGEV-infected cells. Immunofluorescence assays performed both on insect and mammalian cells revealed that ORF4 was a membrane-associated protein, a finding consistent with the prediction of a membrane-spanning segment in ORF4 sequence. Two epitopes were localized within the last 21 C-terminal residues of the sequence through peptide scanning and analysis of the reactivity of a truncated ORF4 recombinant protein. Since the relevant MAbs were found to induce a cell surface fluorescence, these data suggest that ORF4 may be an integral membrane protein having a Cexo-Nendo orientation. Anti-ORF4 MAbs were also used to show that ORF4 polypeptide may be detected in TGEV virion preparations, with an estimated number of 20 molecules incorporated per particle. Comparison of amino acid sequence data provided strong evidence that other coronaviruses encode a polypeptide homologous to TGEV ORF4. Our results led us to propose that ORF4 represents a novel minor structural polypeptide, tentatively designated SM (small membrane protein).

Field Isolates of Transmissible Gastroenteritis Virus Differ at the Molecular Level from the Miller and Purdue Virulent and Attenuated Strains and from Porcine Respiratory Coronaviruses.

“…proposed as a viral membrane-associated minor structural polypeptide [13]. Other mRNAs, 3,5, and 8 are assumed to encode nonstructural proteins.…”

Sequence and expression of the ns2 protein gene of human coronavirus OC43

“…Human coronavirus OC43 comprises four or five major structural proteins: a peplomer (S) glycoprotein, an haemagglutinin-esterase (HE) glycoprotein, a nucleocapsid (N) phosphoprotein and a membrane (M) glycoprotein (Mounir & Talbot, 1992, 1993aZhang et al, 1992;Kamahora et al, 1989), as well as a predicted small membrane protein (sM) (Mounir & Talbot, 1993 b), apparently similar to the one previously identified in virions of infectious bronchitis virus (IBV) and TGEV (Liu & Inglis, 1991, Godet et al, 1992. In addition to these structural proteins, HCV-OC43 possesses several open reading frames (ORF) that could encode putative nonstructural (ns) proteins (Mounir & Talbot, 1993b).…”

Analysis of a 9.6 kb sequence from the 3' end of canine coronavirus genomic RNA

“…0001-1003 © 1992 SGM protein, SM; and the 50K nucleocapsid protein, N (Garwes & Reynolds, 1981 ;Godet et al, 1992).…”