Abstract
Among a variety of fluorescent proteins available today, there is a lack of suitable markers with excitation/emission in the violet/blue part of visible spectrum. Recently, we reported on photoswitchable cyan fluorescent protein (PSβCFP), which represents monomeric highβcontrasting photactivatable label for in vivo protein movement tracking. However, PSβCFP demands high intensity of light for the photoswitching. Therefore it can be employed as a common fluorescent tag at conventional light intensities, which cause negligible or zero photoactivation. High pH stability and unique positioning of excitation/emission peaks make it a worthy supplement to the existing palette of fluorescent proteins. Here we use PSβCFP fusion with a yellow fluorescent protein phiYFP to show that PSβCFP is a promising donor partner for the fluorescence resonance energy transfer (FRET). A remarkable phenomenon is that PSβCFP donor fluorescence turned to be essentially stable with and without FRET, while acceptor emission demonstrated record dynamic range of up to 7.8βfold. This makes the FRET pair presented a useful tool for the single color high throughput screenings. Here we also propose ways for further PSβCFP enhancing, aiming to develop bright cyan fluorescent protein with unique spectral characteristics. Microsc. Res. Tech. 69:207β209, 2006. Β© 2006 WileyβLiss, Inc.