Transcription factor 15Transcription factor 15 also known as Paraxis, is a protein that in humans is encoded by the TCF15 gene.FunctionTranscription factor 15 is found in the nucleus and is involved in the early transcriptional regulation of patterning of the mesoderm, and has a key role in somitogenesis. The encoded basic helix-loop-helix protein requires dimerization with another basic helix-loop-helix protein for efficient DNA binding. .