Crystallization and preliminary X-ray diffraction analysis of the CRISPR-Cas RNA-silencing Cmr complex

Clustered regularly interspaced short palindromic repeat (CRISPR)-derived RNA (crRNA) and CRISPR-associated (Cas) proteins constitute a prokaryotic adaptive immune system (CRISPR-Cas system) that targets and degrades invading genetic elements. The type III-B CRISPR-Cas Cmr complex, composed of the six Cas proteins (Cmr1-Cmr6) and a crRNA, captures and cleaves RNA complementary to the crRNA guide sequence. Here, a Cmr1-deficient functional Cmr (Cmr Delta 1) complex composed of Pyrococcus furiosus Cmr2-Cmr3, Archaeoglobus fulgidus Cmr4-Cmr5-Cmr6 and the 39-mer P. furiosus 7.01-crRNA was prepared. The Cmr Delta 1 complex was cocrystallized with single-stranded DNA (ssDNA) complementary to the crRNA guide by the vapour-diffusion method. The crystals diffracted to 2.1 angstrom resolution using synchrotron radiation at the Photon Factory. The crystals belonged to the triclinic space group P1, with unit-cell parameters a = 75.5, b = 76.2, c = 139.2 angstrom, alpha = 90.3, beta = 104.8, gamma = 118.6 degrees. The asymmetric unit of the crystals is expected to contain one Cmr Delta 1-ssDNA complex, with a Matthews coefficient of 2.03 angstrom(3) Da(-1) and a solvent content of 39.5%.