Fifty-nine RNA duplexes containing single nucleotide bulge loops were optically melted in 1M NaCl, and the thermodynamic parameters ΔH°, ΔS°, ΔG°3 7 , and T M for each sequence were determined. Sequences from this study were combined with sequences from previous studies (Longfellow et al., (1990) Biochemistry 29, 278-285 andZnosko et al., (2002) Biochemistry 41, 10406-10417), thus examining all possible group I single nucleotide bulge loop and nearest-neighbor sequence combinations. The free energy increments at 37 °C for the introduction of a group I single nucleotide bulge loop ranges between 1.3 and 5.2 kcal/mol. The combined data were used to develop a model to predict the free energy of an RNA duplex containing a single nucleotide bulge. For bulge loops with adjacent Watson-Crick base pairs, neither the identity of the bulge nor the nearest-neighbor base pairs had an effect on the influence of the bulge loop on duplex stability. The proposed model for prediction of the stability of a duplex containing a bulged nucleotide was primarily affected by non-nearestneighbor interactions. The destabilization of the duplex by the bulge was related to the stability of the stems adjacent to the bulge. Specifically, there was a direct correlation between the destabilization of the duplex and the stability of the less stable duplex stem. The stability of a duplex containing a bulged nucleotide adjacent to a wobble base pair also was primarily affected by non-nearest-neighbor interactions. Again, there was a direct correlation between the destabilization of the duplex and the stability of the less stable duplex stem. However, when one or both of the bulge nearest neighbors was a wobble base pair, the free energy increment for insertion of a bulge loop is dependent upon the position and orientation of the wobble base pair relative the bulged nucleotide. Bulge sequences of the type , , and are less destabilizing by 0.6 kcal/mol and bulge sequences of the type and are more destabilizing by 0.4 kcal/mol than bulge loops adjacent to Watson-Crick base pairs.RNA fulfills essential cellular roles including storage of information, protein and small molecule binding, and chemical catalysis (1-10). The functional diversity of RNA is often predicated by hierarchical folding of complex tertiary structures with secondary structure formation preceding that of the native, functional fold (11,12). Since the tertiary structure arises from the preformed secondary structure, accurately determining the secondary structure of an

BACKGROUND The Emergency Surgery Score (ESS) was recently developed and retrospectively validated as an accurate mortality risk calculator for emergency general surgery. We sought to prospectively validate ESS, specifically in the high-risk nontrauma emergency laparotomy (EL) patient. METHODS This is an Eastern Association for the Surgery of Trauma multicenter prospective observational study. Between April 2018 and June 2019, 19 centers enrolled all adults (aged >18 years) undergoing EL. Preoperative, intraoperative, and postoperative variables were prospectively and systematically collected. Emergency Surgery Score was calculated for each patient and validated using c-statistic methodology by correlating it with three postoperative outcomes: (1) 30-day mortality, (2) 30-day complications (e.g., respiratory/renal failure, infection), and (3) postoperative intensive care unit (ICU) admission. RESULTS A total of 1,649 patients were included. The mean age was 60.5 years, 50.3% were female, and 71.4% were white. The mean ESS was 6, and the most common indication for EL was hollow viscus perforation. The 30-day mortality and complication rates were 14.8% and 53.3%; 57.0% of patients required ICU admission. Emergency Surgery Score gradually and accurately predicted 30-day mortality; 3.5%, 50.0%, and 85.7% of patients with ESS of 3, 12, and 17 died after surgery, respectively, with a c-statistic of 0.84. Similarly, ESS gradually and accurately predicted complications; 21.0%, 57.1%, and 88.9% of patients with ESS of 1, 6, and 13 developed postoperative complications, with a c-statistic of 0.74. Emergency Surgery Score also accurately predicted which patients required intensive care unit admission (c-statistic, 0.80). CONCLUSION This is the first prospective multicenter study to validate ESS as an accurate predictor of outcome in the EL patient. Emergency Surgery Score can prove useful for (1) perioperative patient and family counseling, (2) triaging patients to the intensive care unit, and (3) benchmarking the quality of emergency general surgery care. LEVEL OF EVIDENCE Prognostic study, level III.