Sites of phosphorylation on the CTD serve as a recognition or anchor point for other proteins to dock with the polymerase. The capping enzyme (guanylyl transferase), which adds the G residue to the 5' end of newly synthesized mRNA, binds to CTD phosphorylated at serine 5, the first phosphorylation event catalyzed by TFIIH. 

P-TEFb leads to recruitment of a set of proteins called SCAFs to the CTD, and they in turn bind to splicing factors. This may be a means of coordinating transcription and splicing.

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#Id: 6128

#Unit 3. Fundamental Processes

Glycosylase action is followed by the endonuclease APE1, which cleaves the polynucleotide chain on the 5’ side. This in turn attracts a replication complex including the DNA polymerase d/E and ancillary components, which performs a short synthesis reaction extending for two to 10 nucleotides. The displaced material is removed by the endonuclease FEN1.

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#Id: 6129

#Unit 3. Fundamental Processes

When the initial removal involves lyase action, the endonuclease APE1 instead recruits DNA polymerase b to replace a single nucleotide. The nick is then sealed by the ligase XRCC1/ligase-3. This is called the short-patch pathway.

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#Id: 6130

#Unit 3. Fundamental Processes

Alkyladenine DNA glycosylase (AAG), recognizes and removes a variety of alkylated substrates, including 3-methyladenine, 7-methylguanine, and hypoxanthine. 

TLS Online TPP Program

#Id: 6131

#Unit 3. Fundamental Processes

1-methyladenine and 3MC is corrected by an enzyme that uses an oxygenating mechanism alkB by reversal mechanism

TLS Online TPP Program

#Id: 6132

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6133

#Unit 3. Fundamental Processes

The oxoG adduct is highly mutagenic because it can base-pair with adenine as well as with cytosine. If it base-pairs with adenine during replication, it gives rise to a G:C to T:A transversion, which is one of the most common mutations found in human cancers.