Project Summary The goal of this administrative supplement is to acquire key instruments for setting up an in-house sample preparation system to facilitate dynamic studies of large photoreceptor molecules using the cryoEM single particle analysis method. Leveraging on the progress made in the first two years of this funding period, this system will enable direct observation and analytical deconvolution of light-induced conformational dynamics in photoreceptor particles that cannot be obtained by other methods. This experimental capability will allow controlled photoexcitation of light sensitive systems, and ensure the sample quality and consistency critical to the success of dynamic experiments. It will strengthen our ongoing effort of the parent grant that centers on the mechanistic understanding of light signaling and allosteric regulation in modular photoreceptors.