A 4.3kb cis-regulatory region (from position -4428 to -61bp upstream of the mutated hhMrt-RB transcript start site) drives the expression of lacZ under the control of a minimal hsp43 promoter. hhMrt mutants exhibit a 24bp deletion in the 'C' domain of the hh promoter (The 'C' domain is defined as -4265 to -3214bp upstream of the hh-RB transcription start site).