mRNA Cap Formation in Parasitic Protozoa

UB Department of Biological Sciences: Kiong Ho: "mRNA processing plays a critical role in the expression of eukaryotic genes. Processing occurs cotranscriptionally on nascent chains synthesized by RNA polymerase II. The earliest modification event is the addition of m7GpppN cap. This structural hallmark is present on all eukaryotic cellular mRNAs and is essential for viability. The cap enhances several downstream events in gene expression including mRNA stability, splicing of pre-mRNAs, and initiation of protein synthesis.

Structure of Mammalian RNA Triphosphatase

Structure of Fungal RNA Triphosphatase
Cap formation is mediated by three enzymatic reactions in which the 5' triphosphate end of pre-mRNA is hydrolyzed to a 5' diphosphate by RNA triphosphatase, then capped with GMP by RNA guanylyltransferase, and methylated by RNA (guanine-N7) methyltransferase. The sequential steps in the capping reaction are universal to all eukaryotes, yet there is a significant divergence in the catalytic mechanism of the triphosphatase component. Metazoan triphosphatases belong to a superfamily of phosphatases that act via the formation and hydrolysis of a cysteinyl-phosphate intermediate. Fungal and viral triphosphatases comprise a novel family of metal-dependent phosphohydrolases with a unique tertiary structure. "