Disease relevance of RAD18

• Drug toxicity was marginally increased by the presence of rad3 and rad18 mutations [1].
• RAD18(-/-) cells also showed higher levels of H2AX phosphorylation and chromosomal aberrations, particularly chromosomal gaps and breaks, upon exposure to CPT [2].

High impact information on RAD18

• Here, we show that RAD6 forms a specific complex with the product of the DNA repair gene RAD18 [3].
• These data suggest that RAD18 plays an essential role in maintaining chromosomal DNA in cooperation with the RAD54-dependent DNA repair pathway [4].
• Interestingly, elevated sister chromatid exchange, which reflects HR- mediated post-replicational repair, was observed in RAD18(-/-) cells during the cell cycle [4].
• RAD18 and RAD54 cooperatively contribute to maintenance of genomic stability in vertebrate cells [4].
• To investigate the role of RAD18, we disrupted RAD18 by gene targeting in the chicken B-lymphocyte line DT40 [4].

Biological context of RAD18

• We have assessed the effect of bound photolyase on the dark survival of yeast cells carrying mutations in genes that eliminate either nucleotide excision repair (RAD2) or mutagenic repair (RAD18) [5].
• This supports a role for the Rad6-Rad18 protein complex in the control of spontaneous mutagenesis [6].
• On the other hand, we found that the mutator phenotypes caused by deficiency in Rad18 and Rad6, are largely alleviated by defects in proteasome activities [7].
• We show that rad5 and rad18 strains have elevated levels of spontaneous recombination, both of ectopic gene conversion and of recombination between direct repeats [8].
• Specific complex formation between yeast RAD6 and RAD18 proteins: a potential mechanism for targeting RAD6 ubiquitin-conjugating activity to DNA damage sites [3].

Anatomical context of RAD18

• RAD18-independent ubiquitination of proliferating-cell nuclear antigen in the avian cell line DT40 [9].

Associations of RAD18 with chemical compounds

• Our current model suggests that the Rad6-Rad18 complex targets Poleta at DNA gaps that result from the MMR-mediated excision of adenine mispaired with 8-oxoG, allowing error-free dCMP incorporation opposite to this lesion [10].
• We have investigated this mechanism in Saccharomyces cerevisiae, in which it is the major component of the RAD6/RAD18 pathway, by transforming an isogenic set of rad1Delta excision-defective strains with plasmids that carry a single thymine-thymine pyrimidine (6-4) pyrimidinone photoadduct in each strand at staggered positions 28 base pairs apart [11].
• RAD5 also contains a cysteine-rich sequence motif that resembles the corresponding sequences found in 11 other proteins, including those encoded by the DNA repair gene RAD18 and the RAG1 gene required for immunoglobin gene arrangement [12].
• CONCLUSIONS: We have demonstrated that the repair of DNA adducts produced by the highly sequence specific minor groove alkylating agent 3 involves an error free adduct elimination pathway dependent on the Rad18 protein [13].
• In addition, rad9 rad18 is no more sensitive to MMS than the rad18 single mutant, suggesting that rad9 plays a role within the PRR pathway [14].

Physical interactions of RAD18

• The Rad6-Rad18 complex provides the first example wherein a ubiquitin conjugating activity is physically associated with DNA binding and ATPase activities provided by an associated protein factor [15].

Other interactions of RAD18

• GCR suppression by Rad5 and Rad18 appears to be exerted by the RAD5-dependent error-free mode of bypass DNA repair [16].
• This is most clear for the repair of adducts on the transcribed strand, where an absolute requirement for Rad6 and Rad18 was seen [17].
• We propose that Rad18/Rad5/Mms2 and Mgs1 are required to promote replication when forks are destabilized or stalled due to defects in Poldelta [18].
• We also demonstrate that the elimination of this class of minor groove adduct from the active MFA2 gene depends upon functional Rad18 and Rad6 [17].
• The Srs2 helicase plays an important role in creating the recombinogenic substrate(s) processed by the RAD5 and RAD18 gene products [8].

Analytical, diagnostic and therapeutic context of RAD18

• Linkage and allelism tests indicate that the mutation is an allele of the known radiation-sensitive gene rad18 [19].
• Sequence analysis of the mutant allele showed pso8-1 to contain a novel, hitherto undescribed T-->C transition in nucleotide position 191, leading to a substitution by leucine of a highly conserved proline at position 64, Rad6-[P64L], which may have severe consequences for the tertiary structure (and hence binding to Rad18p) of the mutant protein [20].

References