Mature HIV-1 particles contain conical-shaped capsids that enclose the viral RNA genome and perform essential functions in the virus life cycle. Previous structural analysis of two and three-dimensional arrays provided a molecular model of the capsid protein (CA) hexamer and revealed three interfaces. Here, we present a cryoEM study of a tubular assembly of CA and a high-resolution NMR structure of the CA C-terminal domain (CTD) dimer. In the solution dimer structure, the monomers exhibit different relative orientations compared to previous X-ray structures. The solution structure fits extremely well into the EM density map, suggesting that the dimer interface is retained in the assembled CA. We also identified a novel CTD-CTD interface at the local three-fold axis in the cryoEM map and confirmed its functional importance by mutagenesis. In the tubular assembly, CA intermolecular interfaces vary slightly, accommodating the asymmetry present in tubes. This provides the necessary plasticity to allow for controlled virus capsid dis/assembly.