In the absence of allolactose, the repressor is present in a form that binds its site on DNA (and so keeps the lac genes switched off ). 

TLS Online TPP Program

#Id: 3335

#Unit 3. Fundamental Processes

Seven genes have been identified in which mutations give rise to XP, these genes specify proteins (such as XPA, XPC, XPD, XPF, and XPG;)

TLS Online TPP Program

#Id: 3337

#Unit 3. Fundamental Processes

In addition to proteins involved in NER, a variant form of XP called XP-V is caused by a defect in the translesion DNA polymerase, Pol h. The gene encoding Pol h is sometimes called XPV. Individuals with XP-V have a milder form of XP.

TLS Online TPP Program

#Id: 3339

#Unit 3. Fundamental Processes

Cells possessing a mutant Pol h are hindered in their ability to bypass thymine dimers during replication and must resort to using another translesion polymerase for bypass to avoid a block in replication. 

TLS Online TPP Program

#Id: 3346

#Unit 3. Fundamental Processes

Pol h (but not other translesion polymerases) correctly inserts As across from a thymine dimer, the use of other translesion polymerases may increase the frequency of mutagenesis

TLS Online TPP Program

#Id: 3348

#Unit 3. Fundamental Processes

Direct repair of alkylated bases by AlkB

TLS Online TPP Program

#Id: 3349

#Unit 3. Fundamental Processes

The AlkB protein is an alpa-ketoglutarate-Fe2+ dependent hydroxylase. It catalyzes the oxidative demethylation of 1-methyladenine and 3-methylcytosine residues