Aureochrome-1 (AUREO1) has been identified as a blue light (BL) receptor responsible for the BL-induced blanching of a stramenopile alga, Vaucheria frigida. BL induces the dimerization of monomeric AUREO1, which subsequently increases its affinity for the target sequence. We made a synthetic gene encoding N-terminally truncated monomeric AUREO1 (Photozipper protein) containing a basic region/leucine zipper (bZIP) domain and a light-oxygen-voltage-sensing domain. In the present study, yellow fluorescent protein or mCherry protein was fused with the Photozipper (PZ) protein, and their oligomeric structures and DNA-binding were compared in the dark and light states. Dynamic light scattering and size exclusion chromatography demonstrated that the hydrodynamic radii and molecular masses of the fusion proteins increased upon BL illumination, suggesting that fusion PZs underwent BL-induced dimerization. Moreover, BL-induced dimerization enhanced their affinities for the target sequence. Taken together, PZ likely functions as a BL-regulated bZIP module in fusion proteins, and can possibly provide a new approach for controlling bZIP transcription factors.

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A surface structural comparison of composite film of bacteriorhodopsin (BR) and phosphatidylcoline (PC) fabricated on a layered fatty acid film on a substrate of amorphous silicon dioxide (a-SiO 2 ), crystal silicon dioxide (c-SiO 2 ), or hydrogenated amorphous silicon (a-Si:H) was conducted to investigate the effect of substrate structure on the Langmuir-Blodgett (LB) film fabrication of membrane protein by direct force microscopy (DFM) measurement. On the a-SiO 2 substrate, a hexagonal crystal structure of BR and PC with a size of 0.5 mm was observed. However, on the c-SiO 2 or a-Si:H substrate, the surface structural features of the composite LB films differed from each other on the shape of assemblies in themselves. In spite of the presence of fatty acid layers, the assemby of BR and PC depends on the structure of the bottom substrate.

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