After dissociation of the E. coli recBc DNase (ATP-dependent DNase) with concentrated NaCl, two subunit proteins were isolated by ion exchange chromatography. Combination and subsequent incubation of the subunits resulted in the appearance of the original DNase. The subunit proteins, designated α and β, have s 20,ω of 4.1 S and 8.1 S, respectively. The α subunit possesses neither the ATP-dependent Dnase nor the DNA-dependent ATPase of the original enzyme. The β subunit contains a low level of both enzymatic activities in a ratio markedly different from that of the original enzyme. The β subunit complemented extracts from both recB and recC mutant strains to produce recBC DNase, while the α subunit did not complement either extract. These results suggest that recB and recC genes are both required for the production of β subunit and that the recBC DNase molecule contains a protein component (α) that is not determined by either the recB or the recC gene.

Lieberman, R. P., & Oishi, M. (1974). The recBC Deoxyribonuclease of Escherichia coli: Isolation and Characterization of the Subunit Proteins and Reconstitution of the Enzyme. Proceedings of the National Academy of Sciences, 71(12), 4816–4820.