Dimeric rous sarcoma virus capsid protein structure relevant to immature Gag assembly.

The structure of the N-terminal domain (NTD) of Rous sarcoma virus (RSV) capsid protein (CA), with an upstream 25 amino acid residue extension corresponding to the C-terminal portion of the Gag p10 protein, has been determined by X-ray crystallography. Purified Gag proteins of retroviruses can assemble in vitro into virus-like particles closely resembling in vivo-assembled immature virus particles, but without a membrane. When the 25 amino acid residues upstream of CA are deleted, Gag assembles into tubular particles.