Structure of Histone mRNA Stem-Loop, Human Stem-Loop Binding Protein, and 3′hExo Ternary Complex

Abstract

Recognizing a Stem-Loop Structure Metazoan histone messenger RNAs (mRNAs) have a conserved stem-loop (SL) structure at their 3′-end. The stem-loop is bound by the stem-loop binding protein (SLBP), which is required for histone mRNA 3′-end processing, export, stability, and translation. The 3′-5′ exonuclease 3′hExo also binds the SL and trims off three nucleotides. Tan et al. (p. 318 ) determined the high-resolution structure of the SL bound by the RNA-binding domain (RBD) of human SLBP together with human 3′hExo. The conformation of the loop differed substantially from other RNA tetraloops and the SLBP RBD may function as a ruler that can measure the length of the stem. Although the SLBP directly recognizes the guanine base of the second nucleotide of the stem, it appears that SLBP and 3′hExo recognize the unique shape of the SL.