RNA multibranch loops (junctions) are loops from which three or more helices exit. They are nearly ubiquitous in RNA secondary structures determined by comparative sequence analysis. In this study, systems in which two strands combine to form three-way junctions were used to measure the stabilities of RNA multibranch loops by UV optical melting and isothermal titration calorimetry (ITC). These data were used to calculate the free energy increment for initiation of a three-way junction on the basis of a nearest neighbor model for secondary structure stability. Imino proton NMR spectra were also measured for two systems and are consistent with the hypothesized helical structures. Incorporation of the experimental data into the mfold and RNAstructure computer programs has contributed to an improvement in prediction of RNA secondary structure from sequence.
Motivated by recent work in parametric sequence alignment, we study the parameter space for scoring RNA folds and construct an RNA polytope. A vertex of this polytope corresponds to RNA secondary structures with common branching. We use this polytope and its normal fan to study the effect of varying three parameters in the free energy model that are not determined experimentally. Our results indicate that variation of these specific parameters does not have a dramatic effect on the structures predicted by the free energy model. We additionally map a collection of known RNA secondary structures to the RNA polytope.
The variations in the arterial pattern specially in the extremities are common. The trifurcation of brachial artery into radial, ulnar and either common interosseous or median artery are found commonly, but radial recurrent artery as a third branch is very rarely reported. Here we are reporting a rare case of bilateral trifurcation of brachial artery into radial, ulnar and radial recurrent artery in an adult female cadaver found during routing dissection in the department of anatomy.