The messenger RNA decapping and recapping pathway in Trypanosoma

Area of Science:

• Molecular Biology
• Biochemistry
• Parasitology

Background:

• The 5' end of trypanosome mRNA is protected by a cap 4 structure derived from spliced leader (SL) RNA.
• Nuclear capping enzyme (TbCgm1) in Trypanosoma brucei generates the m7G SL RNA cap.

Purpose of the Study:

• To elucidate the enzymatic activities and substrates of the cytoplasmic capping enzyme (TbCe1) in Trypanosoma brucei.
• To identify the decapping enzyme (TbDcp2) involved in mRNA processing and surveillance.

Main Methods:

• Enzyme activity assays for RNA kinase and guanylyltransferase.
• RNA silencing experiments to assess the function of TbCe1.
• Identification and characterization of mRNA decapping enzyme (TbDcp2).

Main Results:

• Cytoplasmic capping enzyme (TbCe1) is bifunctional, acting as a 5'-RNA kinase and guanylyltransferase, essential for generating the ppRNA intermediate.
• TbCe1 preferentially targets SL RNA with a 5'-terminal methylated nucleoside.
• Silencing TbCe1 results in uncapped mRNAs, indicating its role in recapping trans-spliced and decapped mRNAs.
• T. brucei mRNA decapping enzyme (TbDcp2) cleaves m7GDP from capped RNA, generating pRNA, and also acts on unmethylated capped RNA.

Conclusions:

• Established the enzymology of a cytoplasmic recapping pathway in Trypanosoma brucei.
• Identified TbCe1 and TbDcp2 as key catalysts in mRNA processing and cap quality surveillance.
• The findings have broad implications for the functional reactivation of processed mRNA ends.