The kink-turn (K-turn) is a new motif in RNA structure that was identified by examination of the crystal structures of the ribosome. We examined the structural and dynamic properties of this element in free solution. The K-turn RNA exists in a dynamic equilibrium between a tightly kinked conformation and a more open structure similar to a simple bulge bend. The highly kinked form is stabilized by the noncooperative binding of metal ions, but a significant population of the less-kinked form is present even in the presence of relatively high concentrations of divalent metal ions. The conformation of the tightly kinked population is in excellent agreement with that of the K-turn structures observed in the ribosome by crystallography. The end-to-end FRET efficiency of this species agrees closely with that of the ribosomal K-turn, and the direction of the bend measured by comparative gel electrophoresis also corresponds very well. These results show that the tightly kinked conformation of the K-turn requires stabilization by other factors, possibly by protein binding, for example. The K-turn is therefore unlikely to be of itself a primary organizing feature in RNA.

The kink-turn is a widespread motif in RNA consisting of a three-nucleotide bulge flanked on one side by consecutive AÁG mismatches. Important examples are found in the ribosome, U4 RNA, and in snoRNAs involved in RNA modification. The motif is a common protein binding site, and the RNA has been found to adopt a tightly kinked conformation in crystal structures. However, in free solution there is a dynamic exchange between kinked and extended conformations, with the equilibrium driven toward the kinked form by the addition of metal ions. Here we used fluorescence resonance energy transfer (FRET) to show that the L7Ae protein of Archaeoglobus fulgidus binds to RNA containing a kink-turn with nanomolar affinity, and induces folding into the tightly kinked conformation even in the absence of metal ions. Thus this RNA may act as a relatively flexible hinge during RNA folding, until fixed into its ultimate kinked structure by the binding of L7 or related protein.

The medial rotation contracture caused by weak external rotation secondary to obstetric brachial plexus injury leads to deformation of the bones of the shoulder. Scapular hypoplasia, elevation and rotation deformity are accompanied by progressive dislocation of the humeral head. Between February and August 2005, 44 children underwent a new surgical procedure called the 'triangle tilt' operation to correct this bony shoulder deformity. Surgical levelling of the distal acromioclavicular triangle combined with tightening of the posterior glenohumeral capsule (capsulorrhaphy) improved shoulder function and corrected the glenohumeral axis in these patients. The posture of the arm at rest was improved and active external rotation increased by a mean of 53 degrees (0 degrees to 115 degrees ) in the 40 children who were followed up for more than one year. There was a mean improvement of 4.9 points (1.7 to 8.3) of the Mallet shoulder function score after surgical correction of the bony deformity.

No abstract

No abstract