Fig. 7.

Proposed model of mRNA decapping and recapping in T. brucei. Nascent SL RNA with 5′ triphosphate end is converted to diphosphate by RNA triphosphatase (TbCet1), capped and methylated by a nuclear capping enzyme (TbCgm1), and hypermethylated by a series of cap 4 methyltransferases (collectively indicated as cap 4 MTases). Trans-spliced and polyadenylated cap 4 mRNA can enter the translational pool, whereas unmethylated capped and hypomethylated capped mRNA are subject to either 3′-to-5′ degradation (not shown) or converted into pRNA by a decapping enzyme (TbDcp2). The decapped pRNA can either be degraded by a 5′-3′ exonuclease, or have its 5′ cap restored by TbCe1 and TbCmt1 and then return to the translational pool.