X-box binding protein 1, also known as XBP1, is a protein which in humans is encoded by the XBP1 gene.
The XBP1 gene is located on chromosome 22 while a closely related pseudogene has been identified and localized to chromosome 5.
The XBP1 protein is a transcription factor that regulates the expression of genes important to the proper functioning of the immune system and in the cellular stress response.