We describe the analysis of two cis-dominant mutations that result in constitutive expression of the inducible CAR1 gene from yeast. One mutation results from insertion of a Ty element just upstream from the point where CAR1-specific transcription begins. The other mutation is a C-to-G transversion at position -153. Isolation of this point mutation, outside of the transcribed region of CAR1, suggests that expression of this gene is regulated at transcription. It also demonstrates the feasibility and usefulness of analyzing the regulatory sequences of eukaryotic genes on a nucleotide-by-nucleotide basis.