Decapping of mRNA containing the histone 3′‐stem loop requires recruitment of stem loop binding protein (SLBP)

Abstract

Modifications at the 5' and 3' ends of eukaryotic mRNA determine both mRNA stability and translational efficiency. One pathway for mRNA degradation involves decapping by Dcp2. We previously developed a phosphorothioate cap analog, m27.2'−OGppspG (S‐ARCA), that is resistant to Dcp2 and confers a longer in vivo half‐life when incorporated into mRNA, indicating that decapping contributes to degradation of polyadenylated mRNAs (Grudzien et al., RNA 13, 1745, 2007). We have now extended this to the 3′‐terminal stem loop (SL) of histone mRNA. The SL is recognized by the stem loop binding protein (SLBP), which is required for the regulation of mRNA processing, turnover, and translation. Luciferase mRNA containing the 5′‐S‐ARCA and 3′‐SL (S‐ARCA‐Luc‐SL) had a 1.8‐fold longer half‐life when introduced into HeLa cells than ARCA‐Luc‐SL, indicating that degradation of SL‐containing mRNAs also involves decapping. mRNA containing a mutated SL that cannot bind SLBP could not be translated yet had a half‐life that was ~3 fold longer than that of S‐ARCA‐Luc‐SL. Interestingly, the increase in stability was independent of the cap, since both mRNAs had similar half‐lives. This result is consistent with translation being required for rapid degradation of histone mRNA, and with SLBP playing a role in the recruitment of the decapping machinery. (Supported by grants No. GM20818 and GM29832 from the NIGMS and No. 55005604 from the HHMI)