RESUMO
4.5S RNA forms with Ffh protein the prokaryotic signal recognition particle (SRP), a highly conserved ribonucleoprotein complex essential for protein secretion. It also independently binds to elongation factor G (EF-G) in the ribosome and has a function in a subset of translocation events that is transient but required for viability. Crystals of three different constructs encompassing the conserved domain IV of 4.5S RNA, containing the recognition elements for both Ffh and EF-G, were obtained. Native X-ray diffraction data were collected for two crystal forms under cryogenic cooling conditions. The best crystals are of a 45 nt construct, diffract anisotropically to 2.6 A resolution using synchrotron radiation and belong to space group P3(2)21, with unit-cell parameters a = b = 69.1, c = 84.6 A and a single RNA molecule per asymmetric unit.