Ribonuclease P (RNase P) is an RNA processing enzyme essential for production of functional tRNAs. Bacterial RNase P is a ribozyme, i.e., an RNA-based enzyme, which functions in all bacteria including those growing at high temperatures (>= 55 degrees C). We examined three bacterial RNase P ribozymes, one from a mesophilic bacterium and two from thermophilic bacteria, to understand the factor(s) providing efficient catalytic ability under conditions of high temperature. Thermophilic RNase P ribozymes show structural adaptations to allow correct folding at high temperature. The presence of a molecular crowder significantly enhanced the catalytic efficiency of thermophilic RNase P ribozyme reactions at 55 degrees C, while it modestly reduced the upper limit of the reaction temperature. (C) 2019 Elsevier Inc. All rights reserved.