In contrast to cells with normal repair capability,<unk> A and<unk> B deficient cells are unable to preferentially repair cyclobutane pyrimidine dimers induced by the action of ultraviolet (UV) light on the template strand of actively transcribed genes. This deficiency reflects the loss of ability to perform the DNA repair process known as transcription coupled nucleotide excision repair (TC-NER). Within the damaged cell, the<unk> A protein normally localizes to sites of DNA damage, particularly inter-strand cross-links, double-strand breaks and some monoadducts.<unk> B protein is also normally recruited to DNA damaged sites, and its recruitment is most rapid and robust as follows: interstrand crosslinks > double-strand breaks > monoadducts > oxidative damage.<unk> B protein forms a complex with another DNA repair protein, SNM1A (DCLRE1A), a 5' – 3' exonuclease, that localizes to inter-strand cross-links in a transcription dependent manner. The accumulation of<unk> B protein at sites of DNA double-strand breaks occurs in a transcription dependent manner and facilitates homologous recombinational repair of the breaks. During the G0/G1 phase of the cell cycle, DNA damage can trigger a<unk> B-dependent recombinational repair process that uses an RNA (rather than DNA) template. The premature aging features of<unk>  are likely due, at least in part, to the deficiencies in DNA repair (see DNA damage theory of aging).
Cockayne syndrome
Xeroderma pigmentosum
ATR-X syndrome
ATR-16 syndrome
Cornelia de Lange syndrome
MEDNIK syndrome
Treacher Collins syndrome
LIG4 syndrome