Figure 1. Capping and decapping pathways.
The 5' end of all RNA polymerase II transcripts is modified with a 7mGpppN cap. The required enzymes of the synthesis pathway are depicted in green. Either the fully formed cap or its precursors can be removed by various decapping enzymes (red). Alternatively, after the bulk of the transcript is degraded by an exonuclease, the residual 7mGpppN cap structure can be degraded by the scavenging decapping enzyme (DcpS). For comparison, the bacterial RNA pyrophosphatase RppH (blue) is included.