Characterization of the lac repressor species produced by limited tryptic cleavage

Tryptic cleavage of native lac repressor under very mild conditions has been found to yield preparations suitable for detailed physical and chemical analysis. Sephadex G-200 chromatography of the digest produces one main protein peak followed by small peptides. The protein from the main peak was analyzed by automated Edman degradation and revealed two unique cleavage sites, one at residue 51 and the other at 59. The tryptic core protein under native conditions is tetrameric and exhibits a circular dichroism spectrum similar to that of native lac repressor.