An exemption from the requirement of a tolerance is established for residues of individual harpin proteins that meet specified physiochemical and toxicological criteria when used as biochemical pesticides on all food commodities to enhance plant growth, quality and yield, to improve overall plant health, and to aid in pest management. The physiochemical and toxicological criteria identifying harpin proteins are as follows:

(a) Consists of a protein less than 100 kD in size, that is acidic (pI<7.0), glycine rich (>10%), and contains no more than one cystine residue.

(b) The source(s) of genetic material encoding the protein are bacterial plant pathogens not known to be mammalian pathogens.

(c) Elicits the hypersensitive response (HR) which is characterized as rapid, localized cell death in plant tissue after infiltration of harpin into the intercellular spaces of plant leaves.

(d) Possesses a common secondary structure consisting of α and β units that form an HR domain.

(e) Is heat stable (retains HR activity when heated to 65 °C for 20 minutes).

(f) Is readily degraded by a proteinase representative of environmental conditions (no protein fragments >3.5 kD after 15 minutes degradation with Subtilisin A).

(g) Exhibits a rat acute oral toxicity (LD50) of greater than 5,000 mg product/kg body weight.

[69 FR 24996, May 5, 2004]