A fast selenium derivatization strategy for crystallization and phasing of RNA structures

Site-specific 2'-methylseleno RNA labeling is a promising tool for tackling the phase problem in RNA crystallography. We have developed an efficient strategy for crystallization and structure determination of RNA and RNA/protein complexes based on preliminary crystallization screening of 2'-OCH3-modified RNA sequences, prior to the replacement of 2'-OCH3 groups with their 2'-SeCH3 counterparts. The method exploits the similar crystallization properties of 2'-OCH3- and 2'-SeCH3-modified RNAs and has been successfully validated for two test cases. In addition, our data show that 2'-SeCH3-modified RNA have an increased resistance to X-ray radiolysis in comparison with commonly used 5-halogen-modified RNA, which permits collection of experimental electron density maps of remarkable quality.