Unpredictable variations in meat toughness in the British pig herd remain a concern to the meat industry. Whilst genetics is clearly important, 50% of this variability can be accredited to environmental factors, such as stress. At slaughter the levels of calpastatin (encoded by the CAST gene), a specific inhibitor protein that regulates the calpain proteinases largely responsible for postmortem tenderization, are strongly related to meat toughness. Down-regulation of CAST expression in the days before slaughter therefore provide a practical opportunity to reduce toughness. There are at least three CAST gene promoters (1xa, 1xb and 1u) containing transcription factor motifs sensitive to β-adrenergic stimulation, which can be induced by physiological stress (Parr et al., 2004). The 1u promoter is the predominant form in porcine muscle and the resulting CAST mRNA transcripts are increased in animals treated with the β-agonist clenbuterol (Sensky et al., 2004) or in cells treated with the analogue dibutyryl cAMP (db cAMP) (Sensky et al., 2005). In this study, the functionality of the 1u promoter is further dissected by truncation studies and mutation of potential cAMP responsive elements (CRE).