Runt-related transcription factor 3 is a protein that in humans is encoded by the RUNX3 gene. This gene encodes a member of the runt domain-containing family of transcription factors. A heterodimer of this protein and a beta subunit forms a complex that binds to the core DNA sequence 5'-YGYGGT-3' found in a number of enhancers and promoters, and can either activate or suppress transcription. It also interacts with other transcription factors. It functions as a tumor suppressor, and the gene is frequently deleted or transcriptionally silenced in cancer. Multiple transcript variants encoding different isoforms have been found for this gene. In melanocytic cells RUNX3 gene expression may be regulated by MITF. Most of this literature used RUNX3 promoter methylation status in various cancers as a proxy for its expression. However, quite many genes are known to be methylated in tumor cell genomes, and the majority of these genes are not expressed in the normal tissue of origin of these cancers.