The vast majority of phages, bacterial viruses, possess a tail ensuring host recognition, cell wall perforation and safe viral DNA transfer from the capsid to the host cytoplasm. Long flexible tails are formed from the tail tube protein (TTP) polymerised as hexameric rings around and stacked along the tape measure protein (TMP). Here, we report the crystal structure of T5 TTP pb6 at 2.2 Å resolution. Pb6 is unusual in forming a trimeric ring, although structure analysis reveals homology with all classical TTPs and related tube proteins of bacterial puncturing devices (type VI secretion system and R-pyocin). Structures of T5 tail tubes before and after interaction with the host receptor were determined by cryo-electron microscopy at 6 Å resolution. Comparison of these two structures reveals that host-binding information is not propagated to the capsid through conformational changes in the tail tube, suggesting a role of the TMP in this information transduction process.

Introducing an unprecedented nucleating and phasing agent for protein crystallography that presents convenient luminescence properties.

The behaviour of the d(GGTATACC) oligonucleotide has been investigated by X-ray crystallography at 295 K in the range from ambient pressure to 2 GPa (∼20 000 atm). Four 3D-structures of the A-DNA form (at ambient pressure, 0.55, 1.09 and 1.39 GPa) were refined at 1.60 or 1.65 Å resolution. In addition to the diffraction pattern of the A-form, the broad meridional streaks previously explained by occluded B-DNA octamers within the channels of the crystalline A-form matrix were observed up to at least 2 GPa. This work highlights an important property of nucleic acids, their capability to withstand very high pressures, while keeping in such conditions a nearly invariant geometry of base pairs that store and carry genetic information. The double-helix base-paired architecture behaves as a molecular spring, which makes it especially adapted to very harsh conditions. These features may have contributed to the emergence of a RNA World at prebiotic stage.