Group I intron ribozymes share common core elements that form a three-dimensional structure responsible for their catalytic activity. This core structure is unstable without assistance from additional factors that stabilize its tertiary structure. We examined biogenic triamine and tetraamine and also their fragments for their abilities to stabilize a structurally unstable group I ribozyme, Delta P5 ribozyme, derived from the Tetrahymena group I intron ribozyme by deleting its large activator module. Biogenic triamine (spermidine) and tetraamine (spermine) efficiently activated the Delta P5 ribozyme under conditions where the ribozyme was virtually inactive. These observations suggested that polyamines are promising small molecule modulators to activate and possibly inhibit the core catalytic ability of group I ribozymes. (C) 2018 Elsevier Inc. All rights reserved.