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A new, inherently flexible, predominantly α-helical RNA binding motif has been detected in two rather conserved ribosomal proteins. Comparative studies prompt the suggestion that these ribosomal proteins are the ancestors of this new helix-turn-helix fold, also found in homeodomains.
A new view of protein folding kinetics replaces the idea of ‘folding pathways’ with the broader notions of energy landscapes and folding funnels. New experiments are needed to explore them.
The structure of the ribosomal protein S15 reveals a novel predominantly α-helical fold and allows for a prediction of the RNA binding surface and orientation within the assembled ribosome.
The RNA binding domain of ribosomal protein L11 is strikingly similar to the homeodomain class of eukaryotic DNA binding proteins: it contains three α-helices that superimpose with homeodomain α-helices, and some conserved residues required for rRNA recognition align with homeodomain helix III residues contacting DNA bases.
The C-terminal DNA-binding domain of OmpR, a positive regulator involved in osmoregulation expression of the ompF and ompC genes in Escherichia coli, has a helix-turn-helix variant motif. The ‘turn’ region, consisting of 11 residues, forms an RNA polymerase contact site.
Transfection studies with cDNAs encoding hybrids between the highly similar cytochrome P450 enzymes, CYP11B1 (steroid 11β-hydroxylase) and CYP11B2 (aldosterone synthase) have identified which amino acids determine the different activities of the enzymes.
The structure of fructose 1,6-bisphosphate aldolase shows three distinct modes of product binding that are correlated to the disposition of the C-terminal region and depicts a possible trajectory for product exchange. The structure also indicates binding preference for monobasic triose phosphates.
Electron cryo-microscopy and image analysis of frozen-hydrated, two-dimensional crystals of gap junction membrane channels formed by recombinant α1 connexin (Cx43) reveal a ring of transmembrane α-helices that lines the aqueous pore and a second ring of α-helices in close contact with the membrane lipids.
