Structural studies show that the active site of DNA Pol h is better at accommodating a thymine dimer than is the active site of another translesion DNA polymerase (DNA Pol k

#Id: 3359

#Unit 3. Fundamental Processes

Another example of direct reversal is the removal of the methyl group from the methylated base O6 –methylguanine  In this case, a methyltransferase removes the methyl group from the guanine residue by transferring it to one of its own cysteine residues. This is costly to the cell because the methyltransferase is not catalytic; having once accepted a methyl group, it cannot be used again.

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#Unit 3. Fundamental Processes

#Id: 3363

#Unit 3. Fundamental Processes

The two chromophores in E. coli photolyase (Mr 54,000), N5 N10-methenyltetrahydrofolylpolyglutamate (MTHF polyGlu) and FADH , perform complementary functions.

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#Unit 3. Fundamental Processes

In reversal, MTHF polyGlu functions as a photoantenna to absorb blue-light photons.

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#Unit 3. Fundamental Processes

In E. coli, DNA Pol IV (DinB) or DNA Pol V (a complex of the proteins UmuC and UmuD0 ) performs translesion synthesis. 

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#Unit 3. Fundamental Processes

DinB and UmuC are members of a distinct family of DNA polymerases found in many organisms known as the Y family of DNA polymerases. There are five translesion polymerases known in humans, four of which belong to the Y family.