Active site of the mRNA-capping enzyme guanylyltransferase from Saccharomyces cerevisiae: similarity to the nucleotidyl attachment motif of DNA and RNA ligases.

AUTOR(ES)

Fresco, L D

RESUMO

Nascent mRNA chains are capped at the 5' end by the addition of a guanylyl residue to form a G(5')ppp(5')N ... structure. During the capping reaction, the guanylyltransferase (GTP:mRNA guanylyltransferase, EC 2.7.7.50) is reversibly and covalently guanylylated. In this enzyme-GMP (E-GMP) intermediate, GMP is linked to the epsilon-amino group of a lysine residue via a phosphoamide bond. Lys-70 was identified as the GMP attachment site of the Saccharomyces cerevisiae guanylyltransferase (encoded by the CEG1 gene) by guanylylpeptide sequencing. CEG1 genes with substitutions at Lys-70 were unable to support viability in yeast and produced proteins that were not guanylylated in vitro. The CEG1 active site exhibits sequence similarity to the active sites of viral guanylyltransferases and polynucleotide ligases, suggesting similarity in the mechanisms of nucleotidyl transfer catalyzed by these enzymes.

Documentos Relacionados

• Covalent catalysis in nucleotidyl transfer reactions: essential motifs in Saccharomyces cerevisiae RNA capping enzyme are conserved in Schizosaccharomyces pombe and viral capping enzymes and among polynucleotide ligases.
• Identification of the DNA sequences encoding the large subunit of the mRNA-capping enzyme of vaccinia virus.
• Location of the active site for enzyme-adenylate formation in DNA ligases.
• Mammalian capping enzyme complements mutant Saccharomyces cerevisiae lacking mRNA guanylyltransferase and selectively binds the elongating form of RNA polymerase II
• A Saccharomyces cerevisiae RNA 5'-triphosphatase related to mRNA capping enzyme.