Monday, August 4, 2014

Normal function of the XPD / ERCC2 gene

The ERCC2 gene provides instructions for making a protein called XPD. This protein is an essential subunit of a group of proteins known as the general transcription factor IIH (TFIIH) complex. The TFIIH complex has two major functions:

1) It is involved in a process called gene transcription
2) It helps repairing damaged DNA.

Gene transcription is the first step in protein production. By controlling gene transcription, the TFIIH complex helps regulate the activity of many different genes. The XPD protein appears to stabilize the TFIIH complex. Studies suggest that the XPD protein works together with XPB, another protein in the TFIIH complex that is produced from the ERCC3 gene, to initiate gene transcription.

The TFIIH complex also plays an important role in repairing damaged DNA, which can be damaged by ultraviolet (UV) rays from the sun and by toxic chemicals, radiation, and unstable molecules called free radicals. DNA damage occurs frequently but normal cells are usually able to fix it before it can cause problems ¾ with the help of nucleotide excision repair (NER) mechanism. As part of this repair mechanism, the TFIIH complex separates the section of double-stranded DNA which surrounds the damage. The XPD protein helps with this process by acting as a helicase, which is an enzyme that attaches to particular regions of DNA and temporarily unwinds the two spiral strands. Once the damaged region has been exposed, other proteins excise the abnormal section and replace the damaged area with the correct DNA.

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