A 4.16kbp cis-regulatory region of the hh promoter from the hhMrt allele (from -4265 to -105bp upstream of the hh-RB transcription start site) drives expression of lacZ coding sequences also 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).