Identification of critical residues for RNA binding of nairovirus nucleoprotein

ABSTRACT Orthonairovirus haemorrhagiae (CCHFV) is a tick-borne virus of the Orthonairovirus genus. CCHFV nucleoprotein binds to the viral genomic RNA, which is essential for transcription and replication. Based on structural analyses, several residues located in positively-charged regions of CCHFV nucleoprotein have been indicated to be important for RNA binding. We investigated the effects of each residue on RNA binding using Orthonairovirus hazaraense (HAZV), a surrogate model for CCHFV, to address the lack of detailed investigations. RNA immunoprecipitation assay revealed that the four basic amino acid residues (R59, R178, K414, and K465) are critical for RNA binding. All of these residues are located within the same positively-charged region. Basicity of these residues was also found to be necessary for RNA binding. Recombinant HAZVs carrying RNA binding-defective mutants of nucleoprotein could not be rescued. We identified the critical residues for RNA binding of nairovirus nucleoprotein. This study provides new insights into a detailed binding model between nairovirus nucleoprotein and its genomic RNA. IMPORTANCE We sought to identify the important residues for RNA binding of nairovirus nucleoprotein using Orthonairovirus hazaraense, a surrogate model for Orthonairovirus haemorrhagiae. The four basic amino acid residues of Orthonairovirus hazaraense nucleoprotein were critical for RNA binding. Sufficient RNA-binding capacity of nucleoprotein was essential for successful virus replication. This study provides new insights into a detailed binding model between nairovirus nucleoprotein and its genomic RNA.