Abstract
BackgroundUukuniemi virus (UUKV) belongs to the Phlebovirus genus in the family Bunyaviridae. As a non-pathogenic virus for humans UUKV has served as a safe model bunyavirus in a number of studies addressing fundamental questions such as organization and regulation of viral genes, genome replication, structure and assembly. The present study is focused on the oligomerization of the UUKV nucleocapsid (N) protein, which plays an important role in several steps of virus replication. The aim was to locate the domains involved in the N protein oligomerization and study the process in detail.ResultsA set of experiments concentrating on the N- and C-termini of the protein was performed, first by completely or partially deleting putative N-N-interaction domains and then by introducing point mutations of amino acid residues. Mutagenesis strategy was based on the computer modeling of secondary and tertiary structure of the N protein. The N protein mutants were studied in chemical cross-linking, immunofluorescence, mammalian two-hybrid, minigenome, and virus-like particle-forming assays. The data showed that the oligomerization ability of UUKV-N protein depends on the presence of intact α-helices on both termini of the N protein molecule and that a specific structure in the N-terminal region plays a crucial role in the N-N interaction(s). This structure is formed by two α-helices, rich in amino acid residues with aromatic (W7, F10, W19, F27, F31) or long aliphatic (I14, I24) side chains. Furthermore, some of the N-terminal mutations (e.g. I14A, I24A, F31A) affected the N protein functionality both in mammalian two-hybrid and minigenome assays.ConclusionsUUKV-N protein has ability to form oligomers in chemical cross-linking and mammalian two-hybrid assays. In mutational analysis, some of the introduced single-point mutations abolished the N protein functionality both in mammalian two-hybrid and minigenome assays, suggesting that especially the N-terminal region of the UUKV-N protein is essential for the N-N interaction.
Highlights
IntroductionAs a nonpathogenic virus for humans UUKV has served as a safe model bunyavirus in a number of studies addressing fundamental questions such as organization and regulation of viral genes, genome replication, structure and assembly
Uukuniemi virus (UUKV) belongs to the Phlebovirus genus in the family Bunyaviridae
Since earlier studies on hantaviruses, Rift Valley fever virus (RVFV), and Bunyamwera virus (BUNV) showed that the very terminal regions of the N protein are especially important for the oligomerization [16,20,23,25], we focused on these regions
Summary
As a nonpathogenic virus for humans UUKV has served as a safe model bunyavirus in a number of studies addressing fundamental questions such as organization and regulation of viral genes, genome replication, structure and assembly. UUKV was first isolated from ticks in Uukuniemi, Finland, in 1959 [2], and as a non-pathogenic virus for humans [3], UUKV has served as a safe model bunyavirus in a number of studies addressing fundamental questions, e.g. organization and the viral genome [8]. N protein 3D-structures for four viruses were solved recently - rabies and vesicular stomatitis viruses (Rhabdoviridae) [12,13], Borna disease virus (Bornaviridae) [14], and influenza A virus [15] revealing the oligomerization domains in detail
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