Repressors are trans-acting

The recessive nature of I⁻ mutations demonstrates that the repressor is trans-acting. Although no active repressor is synthesized from the I⁻ gene, the wild-type gene provides a functional repressor that binds to both operators in a diploid cell and blocks lac operon expression (in the absence of an inducer).

ANIMATED ART: I⁻ Lac repressor mutations