Summary
Sequences encoding the N protein of the bovine enteritic coronavirus-F15 strain (BECV-F15) have been cloned in PBR322 plasmid using cDNA produced by priming with oligo-dT on purified viral genomic RNA. Some 265 insert-containing clones were studied. Hybridization of these inserts with poly(A)+ RNA extracted from infected cells led to the conclusion that they were located at the 3′-end of the genome.
After subcloning in M13 phage DNA, clones were sequenced by the Sanger technique. A 1,710-nucleotide sequence corresponding to the gene coding for the viral N-protein was established. It shows 2 overlapping open reading frames (ORF). The 3′-non-coding end of the gene has an 8-nucleotide sequence in common with the homologous genome areas of MHV, TGE and IBV viruses. This sequence may represent the polymerase RNA binding site.
An upstream sequence surrounding the first AUG of the smaller ORF corresponds to a potentially functional initiation codon. The sequence of the primary translation product deduced from the DNA sequence predicts a polypeptide of 207 amino acids (22.9 Kd) with a high leucine (19.8%) content, possessing a hydrophobic N-terminal end.
The larger ORF has a coding capacity of 448 amino acids (49.4 Kd), corresponding to the N-protein molecular weight. The deduced protein possesses 43 serine residues (9.6% of the total amino acid content) which may be phosporylated and involved in N-protein/RNA binding. N-protein also has 5 regions with a high basic amino acid content. One of them is also serine-rich and has a strong homology site with MHV, TGE and IBV viruses. In the first part of the N-terminal, a 12-amino-acid sequence (PRWYFYYLGTGP) is highly conserved for BECV-F15, JHM, TGE and IBV viruses. BCV Mebus strain and BECV-F15 have only minor differences in their N-protein sequence.
Key -Words: Coronavirus, Protein, Nucleocapside, Genome, BECV-F15 strain, N-protein sequence
Résumé
Nous avons cloné l'ARN génomique du coronavirus entéritique bovin F15 (BECV-F15), dans le plasmide PBR322 après avoir préparé le cDNA correspondant à l'aide d'une amorce oligo-dT: 265 clones ont été étudiés. Leur hybridation avec les ARN poly(A)+ extraits des cellules infectées nous a permis de les localiser à l'extrémité 3′-terminale du génome.
Ces clones ont été séquencés par la technique de Sanger, après sous-clonage dans l'ADN du phage M13. Nous avons déterminé une séquence de 1.710 nucléotides correspondant au gène codant pour la protéine N virale. Elle présente deux cadres ouverts de lecture (ORF) chevauchants. On observe à l'extrémité 3′-terminale non codante du génome une séquence de 8 nucléotides observée également dans la région homologue des virus MHV, GET et IBV. Cette séquence pourrait être le site de fixation de l'ARN polymérase.
Le premier AUG du plus petit ORF possède en amont une séquence nucléotidique qui en fait un site d'initiation potentiellement fonctionnel. La séquence du produit primaire de traduction que l'on en déduit est un polypeptide de 207 acides aminés (22,9 Kd) à haute teneur en leucine (19,8%) ayant une extrémité N-terminale hydrophobe.
Le plus grand ORF a une capacité de codage de 448 acides aminés (49,4 Kd), correspondant à la masse moléculaire de la protéine N. La protéine déduite contient 43 résidus sérine (9,6% des acides aminés), qui peuvent être phosphorylés et impliqués dans la liaison entre la protéine N et l'ARN génomique. Cette protéine présente également 5 régions fortement basiques, et l'une d'entre elles est également riche en sérine et a une forte homologie de séquence avec la région homologue des protéines N des virus MHV, GET et IBV. En outre, la première partie de l'extrémité N-terminale montre un enchaînement de 12 acides aminés (PRWYFYYLGTGP) très conservé entre ces quatre même virus.
Les séquences des protéines N de la souche Mebus du BCV et du BECV-F15 ne présentent que des différences mineures.
Mots-clés: Coronavirus, Protéine, Nucléocapside, Génome, Souche BECV-F15, Séquence de la protéine N
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