HEXIM1,also named CLP1,EDG1,HIS1 or MAQ1,is best known as the inhibitor of positive transcription elongation factor b,which regulates the transcription elongation of RNA polymerase II and controls 60-70% of mRNA synthesis. HEXIM1 regulates NF-kappa-B,ESR1,NR3C1 and CIITA-dependent transcriptional activity. Previous studies showed that HEXIM1 interacts with two key p53 regulators,nucleophosmin and HDM2,implying a possible connection between HEXIM1 and the p53 signaling pathway.The mainstream MW of this protein is 70 and 54 kDa. This antibody recognises 54 kDa band.