Relatively few thermodynamic parameters are available for RNA triloops. Therefore, 24 stemloop sequences containing naturally occurring triloops were optically melted, and the thermodynamic parameters ΔH°, ΔS°, ΔG°3 7 , and T M for each stem-loop were determined. These new experimental values, on average, are 0.5 kcal/mol different from the values predicted for these triloops using the model proposed by Mathews et al. [Mathews, D. H., Disney, M. D., Childs, J. L., Schroeder, S. J., Zuker, M., and Turner, D. H. (2004) Proc. Natl. Acad. Sci. USA 101, 7287-7292]. The data for the 24 triloops reported here were then combined with the data for five triloops that were published previously. A new model was derived to predict the free energy contribution of previously unmeasured triloops. The average absolute difference between the measured values and the values predicted using this proposed model is 0.3 kcal/mol. These new experimental data and updated predictive model allow for more accurate calculations of the free energy of RNA stem-loops containing triloops, and, furthermore, should allow for improved prediction of secondary structure from sequence.RNA stem-loops containing three nucleotides in the loop, triloops, are common secondary structure motifs found in naturally occurring RNA. For example, bacterial 16S rRNAs strongly favor tetraloops; however, the UUU triloop is the most common replacement (1). In the 16S-like rRNA variable regions, triloops account for 7% of the loops in bacteria and 16% of the loops in eukaryotes (2). Triloops are also found in large subunit rRNAs (3,4), 5S rRNAs (5), signal recognition particles (6), RNase P RNAs (7), and group I introns (8,9). More specifically, triloops are found in Brome mosaic virus (+) strand RNA (10), human rhinovirus isotype 14 (11), iron responsive element RNA (12), and an RNA aptamer for bacteriophage MS2 coat protein (13), to name a few. Although relatively unstable due to the strain in the loop, triloops may be an important structural feature due to the accessibility of the loop nucleotides for recognition by proteins, other nucleic acids, or small molecules. It has been shown that triloops play a role in various biological processes, including virus replication (11,14), viral synthesis (15), and iron response (12), to name a few. Nevertheless, only a few studies have thermodynamically characterized RNA triloops (16)(17)(18)(19)(20), and only three of these (16-18) were done using 1 M NaCl (the salt concentration in which most nearest neighbor parameters are derived).The current model used by secondary structure prediction algorithms to predict the thermodynamic contribution of RNA triloops to stem-loop stability is sequence independent; all triloops contribute 5.4 kcal/mol to stem-loop stability, with the exception of 5'CCC3' which contributes 6.9 kcal/mol (21). In addition, there are two unstable triloops sequences (5'CAACG3' and 5'GUUAC3') for which this predictive model is not used; instead, the ΔG°3 7,loop values (6.8 and 6.9 kcal/mol, respecti...

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Transfusion after pelvic reconstructive surgery is uncommon. The variables associated with transfusion are preoperative hematocrit <30%, American Society of Anesthesiologists class, bleeding disorders, nonwhite race, Hispanic ethnicity, and concomitant hysterectomy. Recognition of these factors can help guide preoperative counseling regarding transfusion risk after pelvic reconstructive surgery and individualize preoperative preparation.