241 human active and 13 inactive phosphatases in total;
194 phosphatases have substrate data;
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336 protein substrates;
83 non-protein substrates;
1215 dephosphorylation interactions;
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299 KEGG pathways;
876 Reactome pathways;
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last scientific update: 11 Mar, 2019
last maintenance update: 01 Sep, 2023
Bifunctional mRNA-capping enzyme exhibiting RNA 5'-triphosphatase activity in the N-terminal part and mRNAguanylyltransferase activity in the C-terminal part Catalyzes thefirst two steps of cap formation: by removing the gamma-phosphatefrom the 5'-triphosphate end of nascent mRNA to yield adiphosphate end, and by transferring the gmp moiety of GTP to the5'-diphosphate terminus
The mRNA surveillance pathway is a quality control mechanism that detects and degrades abnormal mRNAs. These pathways include nonsense-mediated mRNA decay (NMD), nonstop mRNA decay (NSD), and no-go decay (NGD). NMD is a mechanism that eliminates mRNAs containing premature translation-termination codons (PTCs). In vertebrates, PTCs trigger efficient NMD when located upstream of an exon junction complex (EJC). Upf3, together with Upf1 and Upf2, may signal the presence of the PTC to the 5'end of the transcript, resulting in decapping and rapid exonucleolytic digestion of the mRNA. In the NSD pathway, which targets mRNAs lacking termination codons, the ribosome is believed to translate through the 3' untranslated region and stall at the end of the poly(A) tail. NSD involves an eRF3-like protein, Ski7p, which is hypothesized to bind the empty A site of the ribosome and recruit the exosome to degrade the mRNA from the 3' end. NGD targets mRNAs with stalls in translation elongation for endonucleolytic cleavage in a process involving the Dom34 and Hbs1 proteins.
To facilitate co-transcriptional capping, and thereby restrict the cap structure to RNAs made by RNA polymerase II, the capping enzymes bind directly to the RNA polymerase II. The C-terminal domain of the largest Pol II subunit contains several phosphorylation sites on its heptapeptide repeats. The capping enzyme guanylyltransferase and the methyltransferase bind specifically to CTD phosphorylated at Serine 5 within the CTD. Kinase subunit of TFIIH, Cdk7, catalyzes this phosphorylation event that occurs near the promoter. In addition, it has been shown that binding of capping enzyme to the Serine-5 phosphorylated CTD stimulates guanylyltransferase activity in vitro
The 5'-ends of all eukaryotic pre-mRNAs studied thus far are converted to cap structures. The cap is thought to influence splicing of the first intron, and is bound by 'cap-binding' proteins, CBP80 and CBP20, in the nucleus. The cap is important for translation initiation, and it also interacts with the poly(A)terminus, via proteins, resulting in circularization of the mRNA to facilitate multiple rounds of translation. The cap is also important for mRNA stability, protecting it from 5' to 3' nucleases, and is required for mRNA export to the cytoplasm. The capping reaction usually occurs very rapidly on nascent transcripts; after the synthesis of only a few nucleotides by RNA polymerase II. The capping reaction involves the conversion of the 5'-end of the nascent transcript from a triphosphate to a diphosphate by a RNA 5'-triphosphatase, followed by the addition of a guanosine monophosphate by the mRNA guanylyltransferase, to form a 5'-5'-triphosphate linkage. This cap is then methylated by 2'-O-methyltransferases
To facilitate co-transcriptional capping, and thereby restrict the cap structure to RNAs made by RNA polymerase II, the capping enzymes bind directly to the RNA polymerase II. The C-terminal domain of the largest Pol II subunit contains several phosphorylation sites on its heptapeptide repeats. The capping enzyme guanylyltransferase and the methyltransferase bind specifically to CTD phosphorylated at Serine 5 within the CTD. Kinase subunit of TFIIH, Cdk7, catalyzes this phosphorylation event that occurs near the promoter. In addition, it has been shown that binding of capping enzyme to the Serine-5 phosphorylated CTD stimulates guanylyltransferase activity in vitro
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