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Definition of Isoform
Medically reviewed by Min Clinic Staff | Updated: January 2026
Isoform: A protein that has the same function as another protein but which is encoded by a different gene and may have small differences in its sequence. For example, transforming factor beta (TGF-B) exists in three versions, or isoforms (TGF-B1, TGF-B2, and TGF-B3), each of which can set off a signaling cascade that starts in the cytoplasm and terminates in the nucleus of the cell.