It is synthesized and secreted by the bacterium Bacillus amyloliquefaciens, but is lethal to the cell when expressed without its inhibitor barstar.

The inhibitor binds to and occludes the ribonuclease active site, preventing barnase from damaging the cell's RNA after it has been synthesized but before it has been secreted.

Barnase has no disulfide bonds, nor does it require divalent cations or non-peptide components to fold.

[2][3][4] The folding of barnase has been extensively studied in the laboratory of Alan Fersht, who used it as the test case in developing a method of characterizing protein folding transition states known as phi value analysis.

Although it is not directly involved in acid-base catalysis, Lys27 is also critical for activity; it has been implicated in transition-state substrate binding.