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To achieve the greatest output from their limited genomes, viruses frequently make use of alternative open reading frames, in which translation is initiated from a start codon within an existing gene and, being out of frame, gives rise to a distinct protein product. These alternative protein products are, as yet, poorly characterized structurally. Here we report the crystal structure of ORF-9b, an alternative open reading frame within the nucleocapsid (N) gene from the SARS coronavirus. The protein has a novel fold, a dimeric tent-like beta structure with an amphipathic surface, and a central hydrophobic cavity that binds lipid molecules. This cavity is likely to be involved in membrane attachment and, in mammalian cells, ORF-9b associates with intracellular vesicles, consistent with a role in the assembly of the virion. Analysis of ORF-9b and other overlapping genes suggests that they provide snapshots of the early evolution of novel protein folds.

Original publication

DOI

10.1016/j.str.2006.05.012

Type

Journal article

Journal

Structure

Publication Date

07/2006

Volume

14

Pages

1157 - 1165

Keywords

Amino Acid Sequence, Capsid, Capsid Proteins, Cell Membrane, Crystallography, X-Ray, Evolution, Molecular, Hydrophobic and Hydrophilic Interactions, Molecular Sequence Data, Open Reading Frames, Protein Conformation, Protein Folding, SARS Virus, Virus Assembly