Uridylated Histone mRNA Degradation Intermediates Bind SLBP and 3′hEXO Individually and Together

Abstract

Histone mRNAs are a tightly cell‐cycled regulated group of mRNAs that are strongly expressed at the beginning of S‐phase and rapidly degraded when DNA replication ends. This cell cycle regulation is controlled by histone mRNA's unique 3′ end; instead of the traditional poly(A) tail, histone mRNA instead ends with a 3′ stem‐loop. This stem‐loop is an important factor in controlling the expression and degradation of histone mRNA during S‐phase, along with two key protein binding partners: the stem‐loop binding protein (SLBP) and the human 3′ exonuclease (3′hEXO). At the beginning of degradation, 3′hEXO trims 2 to 7 nucleotides from the 3′ end of the message. These nucleotides are then often replaced by a short uridylation that preserves the length of the stem‐loop. The exact function of these uridylated intermediates and whether they affect histone mRNA metabolism is currently unknown. We characterized the structure of a stem‐loop with seven nucleotides trimmed from the 3′ end and replaced with five uridines using nuclear magnetic resonance (NMR) to show that a stem‐loop still forms, despite this trimming‐and‐replacement mechanism that turns the six‐membered stem into a nine‐membered stem. We also characterized interactions between SLBP, 3′hEXO, and the trimmed and uridylated RNA using electrophoretic mobility shift assays (EMSA) and found that the RNA interacts with both proteins individually and in a ternary complex. As SLBP must dissociate from the stem‐loop before total degradation can progress, the formation of a degradation intermediate that binds SLBP raises new questions about the nature of the interactions and molecular conformation of the uridylated stem‐loop during binding. Additionally, ternary complex formation with the uridylated stem‐loop raises questions as to how these protein/stem‐loop interactions will change upon the addition of known degradation intermediates. Understanding the interactions between a uridylated histone mRNA degradation intermediate and binding proteins will help us better understand the nature of these unique mRNA molecules.Support or Funding InformationThe National Science Foundation CHE‐1659821 (REU)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.