Construction, Isolation and Implications of Repressor‐galactosidase ·ß‐galactosidase Hybrid Molecules

Escherichia coli heterogenotes, which produce hybrid molecules between the chimaeric protein repressor‐galactosidase and the enzyme β‐galactosidase, were constructed. Repressor‐galactosidase. in which fully active lac repressor is covalently linked to active β‐galactosidase, is an aggregate with a core structure of four β‐galactosidase parts and two peripheral lac repressor dimers. The lac repressor dimers, which are separated by tetrameric β‐galactosidase, retain all the biological activities of tetra‐meric lac repressor. Substitution of repressor‐galactosidase subunits with β‐galactosidase subunits leads to hybrid molecules with yβ‐galactosidase subunits aggregated with (4‐y) repressor‐galactosi‐dase subunits (where y= 1, 2 or 3). A 2:2 hybrid, i.e. a tetrameric β‐galactosidase core with one lac repressor dimer grafted to it, binds at least 100 times less strongly to 32P‐labelled λplac DNA than pure lac repressor or repressor‐galactosidase.The data suggest a model in which lac repressor binds with two subunits to lac operator and with the other two subunits elsewhere on the DNA, possibly on sequences like the lac operator.

1. 1
   Lac repressor can be fused to β-galactosidase

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