The retrovirus encoded proteinase (PR) is required for the proper maturation of viral particles into infectious virus. The PR had been considered highly substrate specific, cleaving exclusively the viral gag and gag‐pol protein precursor. It has recently been reported, however, that cytoskeleton and other cellular filament proteins can be cleaved by the HIV‐1 PR. Here we have evidence that a cell‐associated protein, the fibronectin (A‐chain) is also cleaved in vitro specifically by this PR. The possibility of a cytotoxic role of the PR is conceivable.
