Alternative titles; symbolsRAD54, S. CEREVISIAE, HOMOLOG-LIKE HR54HRAD54HGNC Approved Gene Symbol: RAD54LCytogenetic location: 1p34.1 Genomic coordinates (GR...
Alternative titles; symbols
HGNC Approved Gene Symbol: RAD54L
Cytogenetic location: 1p34.1 Genomic coordinates (GRCh38): 1:46,247,687-46,278,476 (from NCBI)
▼ Cloning and Expression
Repair of double-stranded DNA breaks is essential for homologous recombination in somatic cells to protect DNA from damage by ionizing radiation and other genotoxins. The rad52 pathway is required for homologous recombination in the yeast S. cerevisiae. Kanaar et al. (1996) searched for mammalian homologs of yeast rad54, an essential component of this pathway and a member of the rad52 group. Using RT-PCR with degenerate primers, Kanaar et al. (1996) identified the mouse and human homologs of S. cerevisiae rad54. The human homolog, HR54, is 48% identical to the yeast protein and belongs to the SNF2/SWI2 family, which is characterized by amino acid motifs found in DNA-dependent ATPases. Proteins in the SNF2/SWI2 family are involved in many aspects of DNA metabolism, including transcription, repair, and recombination. HR54 protein is located in the nucleus, consistent with its nuclear localization signal and a potential function in DNA metabolism. Expression of HR54 increased approximately 3-fold in late G1 phase; this pattern is similar to that in yeast. HR54 was able to partially complement the DNA repair defect of S. cerevisiae rad54-deleted cells. By Northern blot analysis, Kanaar et al. (1996) showed that expression of the mouse homolog of HR54 is increased in organs of lymphoid and germ cell development. Mouse expression was 3-fold higher in spermatocytes than in spermatids, suggesting that HR54 plays a role in meiotic recombination.
▼ Gene Function
Solinger et al. (2002) showed that RAD54 protein dissociates RAD51 (179617) from nucleoprotein filaments formed on double-stranded DNA (dsDNA). Addition of RAD54 protein overcame inhibition of DNA strand exchange by RAD51 protein bound to substrate dsDNA. Species preference in the RAD51 dissociation and DNA strand exchange assays underlined the importance of specific RAD54-RAD51 protein interactions. RAD51 protein was unable to release dsDNA upon ATP hydrolysis, leaving it stuck on the heteroduplex DNA product after DNA strand exchange. The authors suggested that RAD54 protein is involved in the turnover of RAD51-dsDNA filaments.
Bugreev et al. (2006) showed that RAD54 binds Holliday junction-like structures with high specificity and promotes their bidirectional branch migration in an ATPase-dependent manner. The activity seemed to be conserved in human and yeast Rad54 orthologs. In vitro, Rad54 had been shown to stimulate DNA pairing of Rad51, a key homologous recombination protein. However, genetic data indicated that Rad54 protein might also act at later stages of homologous recombination, after Rad51. Bugreev et al. (2006) concluded that novel DNA branch-migration activity is fully consistent with this late homologous recombination function of Rad54 protein.
Kanaar et al. (1996) mapped the HR54 gene to chromosome 1p32 using fluorescence in situ hybridization.
▼ Molecular Genetics
Association of the recombinational repair protein RAD51 with tumor suppressors BRCA1 (113705) and BRCA2 (600185) suggested that defects in homologous recombination are responsible for tumor formation. This idea was supported by the fact that the protein associated with the MRE11/RAD50 repair complex (NBS1; 602667) is mutated in Nijmegen breakage syndrome (251260), which is characterized by increased cancer incidence and sensitivity to ionizing radiation. Since RAD51 forms a complex with other members of the RAD52 (600392) epistasis group and with BRCA proteins, it was reasonable to ask if alterations of members of the RAD52 epistasis group lead to tumor development. Matsuda et al. (1999) described missense mutations at functional regions of RAD54 and the absence of the wildtype RAD54 expression resulting from aberrant splicing in primary cancers. Since RAD54 is a recombination protein associated with RAD51, this was the first genetic evidence that cancer can arise from a defect in repair processes involving homologous recombination. They observed a pro63-to-his mutation (603615.0001) of the RAD54 gene in an adenocarcinoma of the colon and a val444-to-glu mutation (603615.0002) in a non-Hodgkin lymphoma. Although pro at codon 63 and val at codon 444 are outside helicase motifs, Matsuda et al. (1999) considered it likely that these amino acid substitutions affect the function of RAD54. The mutations demonstrated by Matsuda et al. (1999) were rare among the tumors studied: 95 breast cancers, 13 colorectal cancers, and 24 lymphomas.
▼ ALLELIC VARIANTS ( 3 Selected Examples):
.0001 ADENOCARCINOMA, COLONIC, SOMATIC
In an adenocarcinoma of the colon, Matsuda et al. (1999) found a C-to-A transversion in the RAD54L gene converting pro to his at codon 63, upstream of helicase domains. The corresponding normal tissue showed the wildtype sequence, indicating that this was a somatic mutation.
.0002 LYMPHOMA, NON-HODGKIN, SOMATIC
In non-Hodgkin lymphoma tissue, Matsuda et al. (1999) found a T-to-A transversion converting val to glu at codon 444 between helicase domains III and IV of the RAD54L gene. Because they could not obtain the corresponding normal tissue, they did not know whether this was a germline mutation. The presence of wildtype alleles indicated that this tumor, like the adenocarcinoma of the colon with pro63-to-his (603615.0001) substitution, indicated that these tumors were heterozygous for the mutations.
.0003 BREAST CANCER, INVASIVE DUCTAL
In one of 95 breast cancers studied, Matsuda et al. (1999) found a G-to-A transition in the RAD54L gene converting gly to arg at codon 325 within helicase motif III. The absence of the wildtype allele indicated that the tumor was homozygous (or hemizygous) for the mutation. The corresponding normal tissue showed the same transition, indicating that this was a germline mutation. A restriction-based screen, developed from the fact that the gly325-to-arg mutation abolished an AccIII site, revealed that this mutation was absent in 100 normal individuals. The patient in this case was a 63-year-old woman with no obvious family history of cancer.