Barstar is an intracellular inhibitor of barnase, an extracellular ribonuclease of Bacillus amyloliquefaciens. Barstar binds tightly to the barnase active site and sterically blocks it, thus inhibiting its potentially lethal RNase activity inside the cell. Barstar also binds and inhibits a ribonuclease called RNase Sa (produced by Streptomyces aureofaciens) which belongs to the same enzyme family as does barnase.
Jiyao W et al.(2023). "The conserved domain database in 2023.",