Judge, jury, and executioner: DXO functions as a decapping enzyme and exoribonuclease in pre-mRNA quality control

Abstract

In this issue of Molecular Cell, Jiao et al. (2013) describe the mammalian enzyme DXO, which has pyrophosphohydrolase, decapping, and 5'-3' exoribonuclease activity and functions as an important checkpoint in cotranscriptional capping of RNA polymerase II (Pol II) pre-mRNA transcripts.

Figure 1. Overview of known nuclear decapping activity on nascent pol II transcripts

DXO selectively decaps incompletely capped pre-mRNA, and can also function as the 5′-3′ exonuclease to degrade the RNA transcript body (pink box). Dcp1/2 can remove the m7G cap and trigger transcription termination by the Xrn2-mediated torpedo mechanism (blue box; Brannan et al, 2012). Pol II is RNA polymerase II, CE is the capping enzyme, MT is the guanosine methyltransferase, SAM is S-adenosylmethionine, and CBC is the cap binding complex (CBP80/20).