Besides phot1 and phot2, Arabidopsis has other photosensors containing
LOV domains: FKF1 (flavin-binding Kelch repeat F-box). The function of the F-box
is to interact with SKP proteins, which is important for ubiquitinating
target substrates. Kelch repeat is known to act as a protein-protein interacting
site. FKF1 has been shown to be involved in the light-regulated expression
of CONSTANS (CO), a key gene involved in day-length discrimination leading
to flowering under long-day conditions.
The observed absorption spectral changes upon photoexcitation were similar to the spectral changes observed for typical LOV domain proteins, e.g., phototropins. The adduct formation takes place with a time constant of 6 micros. Following this reaction, a significant conformational change with a time constant of 6 ms was observed as a change in the diffusion coefficient. An FKF1-LOV mutant without the conserved loop connecting helices E and F only present in the FKF1/LKP2/ZTL family did not show these slow phase dynamics. This result indicates that the conformational change in the loop region is a major change of the FKF1-LOV photoreaction.