Characterization of a β-Galactosidase Formed Between a Complementary Protein and a Peptide Synthesized De Novo

Abstract

In a cell-free system, φ80d lac can be transcribed, and the resulting ribonucleic acid can be translated to yield a product which interacts with an enzymatically inactive z protein to produce active enzyme. The inactive z protein is produced by Escherichia coli strain 21, which contains a deletion in the first part of the gene for β-galactosidase and appears to exist as a dimer. The enzyme formed in the cell-free system appears to be composed of one strain 21 z protein dimer and one newly synthesized polypeptide chain with a molecular weight of about 3 × 10 4 . The estimated size of this complementing segment is in good agreement with Ullmann, Jacob, and Monod's estimate of the size of the α region of β-galactosidase. Using α fragments produced by autoclaving or guanidine treatments, we found that the active portion of α seems to be smaller than the full α region. We also found, using α produced by the autoclaving technique, that active dimer undergoes conversion to tetramer as the amount of α is increased. Evidently, the binding of α favors this conversion, but it is unlikely that the conversion of dimer to tetramer per se results in increased enzyme activity.