mApple Fused to Human Annexin A4
A directed evolution approach that selected for enhanced photostability was employed to produce the mApple red fluorescent protein variant, which has spectral characteristics similar to mStrawberry. In addition to its photostability, mApple offers excellent brightness and matures rapidly. The digital image above illustrates the result of transfecting a human cell culture with mApple fused to annexin A4. The annexins are a structurally-distinct family of calcium-regulating proteins. The functions of the annexins are not yet well understood, but annexin A4 is generally thought to have some involvement in exocytosis and epithelial chloride secretion.