Coronaviruses: Structure and Genome Expression

Sequences of 3' end of genome and of 5' end of open reading frame 1a of lactate dehydrogenase-elevating virus and common junction motifs between 5' leader and bodies of seven subgenomic mRNAs

“…irradiation (van Berlo et al, 1982;de Vries et al, 1990). The results differed from those obtained with MHV (Spaan et al, 1988;Yokomori et al, 1992) and suggested that the subgenomic EAV mRNAs are derived from a common genome-length precursor, that is a full-length plus strand (de Vries et al, 1990). Furthermore, it was observed (de Vries et al, 1990) that the segment directly upstream of the proposed junction sequence in the EAV leader (5' UCUCUA 3") is identical to the 5' splice site of the self-splicing pre-rRNA of Tetrahymena and that this segment is followed downstream by an inverted partial complementary sequence (part of ORF la) comparable to the internal guidance sequences of group I introns (Cech, 1990).…”

“…Our data indicate that the formation of the junctions between the 5' leader of LDV and the bodies of its subgenomic mRNAs 1°1 and 2 to 7 is difficult to explain on the basis of the leader-primed transcription mechanism proposed for the synthesis of the subgenomic mRNAs of coronaviruses (Baric et al, 1983;Spaan et al, 1988;Lai, 1990;Yokomori et al, 1992). This model postulates that the plus-strand leader is transcribed by the replicase from a full-length minus-strand antigenome and that the leader then 'falls off' the template and reassociates at complementary sites in intergenic regions downstream in the minus-strand template acting as primer for continued transcription.…”

“…This model postulates that the plus-strand leader is transcribed by the replicase from a full-length minus-strand antigenome and that the leader then 'falls off' the template and reassociates at complementary sites in intergenic regions downstream in the minus-strand template acting as primer for continued transcription. The 3' end of the leader sequence in genomic MHV RNA is composed of two or three repeated 5' UCUAA 3' heptanucleotides followed by a consensus 5' UCUAAAC 3' sequence and two or three repeats of the same or closely related segments are found upstream of the initiation codon of every ORF (Baric et al, 1983;Makino et al, 1986Makino et al, , 1988Makino et al, , 1991Shieh et al, 1987;Spaan et al, 1988;Lai, 1990). For example, the intergenic segment preceding ORF 7 of MHV A59 contains an 18 nucleotide long segment that is identical to the 5' leader sequence.…”

“…However, this conclusion has not been proved and for overlapping ORFs read in different frames readthrough is possible via frameshift mechanisms (Hatfield et al, 1992). Indeed, the ORFs lb of coronaviruses (Spaan et al, 1988 ;Lai, 1990) and EAV (den Boon et al, 1991) seem to be expressed via frameshift processes. In the case of ORFs 2 to 7 of LDV, EAV and LV, however, no established heptanucleotide frameshift signals (slippery sequences) are observed in the overlapping ORF segments and there are no typical downstream stemloop structures, both of which seem to be crucial for frameshifting (Hatfield et al, 1992).…”

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.

“…TGEV belongs to the family Coronaviridae. It is a pleomorphic enveloped virus with a large, single-stranded, positive RNA genome [40,42].…”