RFX1 (regulatory factor X1) is a transcription factor essential for MHC class II gene expression through binding to X-box sequences 1. Located on chromosome 19.1, RFX1 functions as both a transcriptional activator and repressor depending on cellular context 12. The protein contains a characteristic DNA-binding domain and is broadly expressed across multiple tissue types, with particularly high expression in immune, gastrointestinal, reproductive, and nervous systems 2. RFX1 undergoes alternative splicing that can produce isoforms with altered function - exon 2 skipping creates an N-terminal truncated form that loses transcriptional repression ability, leading to oncogene activation 3. Post-translational acetylation by KAT7 regulates RFX1 stability and activity, with acetylation promoting proteasomal degradation and reducing its repressive function on target genes like FGF1 4. Disease relevance includes tumor suppressor roles through c-myc downregulation 5, but also oncogenic functions when dysregulated through hypermethylation in gliomas 5 or aberrant splicing in hepatocellular carcinoma 3. In colon cancer, high RFX1 expression correlates with poor prognosis and altered immune microenvironment 6. Additionally, RFX1 deficiency contributes to neuronal damage in Parkinson's disease through the KAT7/RFX1/FGF1 axis 4.