Calponin 3. acidic is a protein that in humans is encoded by the CNN3 gene. The CNN3 gene is located at 1p22-p21 in the human chromosomal genome. CNN3 gene contains 7 exons and encodes calponin 3, a 36.4-kDa protein consisting of 329 amino acids with isoelectric point (pI) of 5.84. Calponin 3 is known as acidic calponin. Among three isoforms of calponin, less is known for the gene regulation and function of calponin 3. Nonetheless, much has been learned from extensive studies on the homologous genes CNN1 and CNN2 that encode calponin 1 and calponin 2.