A structural overview of retroviral MAs. (A): Structural superimposition of MLV (1MN8), RSV (1A6S) and HIV (1TAM) MA proteins. Superimposition obtained using the combinatorial extension method (CE) and the image was generated with Viewer Pro software (Accelrys), thanks to E. Derivery. (B): Scheme of the [T] to [R] switch. [T] conformation sequesters the myristate of myristylated MAs, and remains monomeric, while [R] conformation associates in trimers and exposes the myristate (when present).