FANCJ mutations are associated with breast cancer and genetically linked to the bone marrow disease Fanconi anemia (FA). The genomic instability of FA-J mutant cells suggests that FANCJ helicase functions in the replicational stress response. A putative helicase with sequence similarity to FANCJ in Caenorhabditis elegans (DOG-1) and mouse (RTEL) is required for poly(G) tract maintenance, suggesting its involvement in the resolution of alternate DNA structures that impede replication. Under physiological conditions, guaninerich sequences spontaneously assemble into four-stranded structures (G quadruplexes [G4]) that influence genomic stability. FANCJ unwound G4 DNA substrates in an ATPase-dependent manner. FANCJ G4 unwinding is specific since another superfamily 2 helicase, RECQ1, failed to unwind all G4 substrates tested under conditions in which the helicase unwound duplex DNA. Replication protein A stimulated FANCJ G4 unwinding, whereas the mismatch repair complex MSH2/MSH6 inhibited this activity. FANCJ-depleted cells treated with the G4-interactive compound telomestatin displayed impaired proliferation and elevated levels of apoptosis and DNA damage compared to small interfering RNA control cells, suggesting that G4 DNA is a physiological substrate of FANCJ. Although the FA pathway has been classically described in terms of interstrand cross-link (ICL) repair, the cellular defects associated with FANCJ mutation extend beyond the reduced ability to repair ICLs and involve other types of DNA structural roadblocks to replication.The identification of FANCJ mutations in early-onset breast cancer patients (3, 34) and Fanconi anemia (FA) group J patients (22,23,25) implicates FANCJ as a tumor suppressor caretaker that ensures genomic stability. FANCJ interacts with the tumor suppressor BRCA1 (3) and is a DNA helicase that catalytically unwinds duplex DNA in an ATP hydrolysis-dependent manner (2, 14). FA-J cells are hypersensitive to interstrand cross-linking (ICL) agents (1, 25); untreated FA-J cells exhibit diminished BRCA1 foci, and the cells show delayed formation of ionizing radiation-induced BRCA1 foci (31). In response to DNA damage or replicational stress, FANCJ colocalizes with the single-stranded DNA (ssDNA) binding protein replication protein A (RPA), which serves as an auxiliary factor for the unwinding function of FANCJ (15). FANCJ interacts with the mismatch repair complex MutL␣, and this interaction is required for the correction of the ICL response in FA-J cells (32). The activation of FANCJ helicase activity is required for timely progression through S phase of the cell cycle (20); however, the precise functions of the FANCJ helicase in S-phase progression remain to be understood.Although a role for FANCJ in DNA replication has been proposed previously, definitive evidence for a role of the FANCJ helicase in preventing genomic instability is lacking. One source of genomic instability is alternate DNA structures that may impede the replication fork. Guanine-rich nucleic acids have the potential to f...

It has been proposed that guanine-rich DNA forms four-stranded structures in vivo called G-quadruplexes or G4 DNA. G4 DNA has been implicated in several biological processes, but tools to study G4 DNA structures in cells are limited. Here we report the development of novel murine monoclonal antibodies specific for different G4 DNA structures. We show that one of these antibodies designated 1H6 exhibits strong nuclear staining in most human and murine cells. Staining intensity increased on treatment of cells with agents that stabilize G4 DNA and, strikingly, cells deficient in FANCJ, a G4 DNA-specific helicase, showed stronger nuclear staining than controls. Our data strongly support the existence of G4 DNA structures in mammalian cells and indicate that the abundance of such structures is increased in the absence of FANCJ. We conclude that monoclonal antibody 1H6 is a valuable tool for further studies on the role of G4 DNA in cell and molecular biology.

Far western blotting (WB) was derived from the standard WB method to detect protein-protein interactions in vitro. In Far WB, proteins in a cell lysate containing prey proteins are firstly separated by SDS or native PAGE, and transferred to a membrane, as in a standard WB. The proteins in the membrane are then denatured and renatured. The membrane is then blocked and probed, usually with purified bait protein(s). The bait proteins are detected on spots in the membrane where a prey protein is located if the bait proteins and the prey protein together form a complex. Compared with other biochemical binding assays, Far WB allows prey proteins to be endogenously expressed without purification. Unlike most methods using cell lysates (e.g., co-immunoprecipitation (co-IP)) or living cells (e.g., fluorescent resonance energy transfer (FRET)), Far WB determines whether two proteins bind to each other directly. Furthermore, in cases where they bind to each other indirectly, Far WB allows the examination of candidate protein(s) that form a complex between them. Typically, 2-3 d are required to carry out the experiment.

Alternate DNA structures that deviate from B‐form double‐stranded DNA such as G‐quadruplex (G4) DNA can be formed by sequences that are widely distributed throughout the human genome. G‐quadruplex secondary structures, formed by the stacking of planar quartets composed of four guanines that interact by Hoogsteen hydrogen bonding, can affect cellular DNA replication and transcription, and influence genomic stability. The unique metabolism of G‐rich chromosomal regions that potentially form quadruplexes may influence a number of biological processes including immunoglobulin gene rearrangements, promoter activation and telomere maintenance. A number of human diseases are characterized by telomere defects, and it is proposed that G‐quadruplex structures which form at telomere ends play an important role in telomere stability. Evidence from cellular studies and model organisms suggests that diseases with known defects in G4 DNA helicases are likely to be perturbed in telomere maintenance and cellular DNA replication. In this minireview, we discuss the connections of G‐quadruplex nucleic acids to human genetic diseases and cancer based on the recent literature.

Background: Mutations in ChlR1 (DDX11) are linked to Warsaw breakage syndrome. Results: ChlR1 unwinds forked duplex, 5Ј flap, D-loop, and two-stranded antiparallel G-quadruplex substrates, whereas a patient-derived mutation abolishes helicase activity. Conclusion: ChlR1 helicase unwinds key intermediates of DNA replication and recombination. Significance: Inactivation of catalytic activity by Warsaw breakage syndrome mutation suggests that ChlR1 helicase function is important in vivo.

SummaryHeterotrimeric G-proteins transduce signals from activated G-protein-coupled receptors (GPCR) to appropriate downstream effectors and thereby play an important role in signaling. A role of G-proteins in salinity and heat stress tolerance has not heretofore been described. We report isolation of cDNAs of two isoforms of Ga (Ga1, 1152 bp; Ga2, 1152 bp), one Gb (1134 bp), two isoforms of Gc (Gc1, 345 bp; Gc2, 303 bp) and a GPCR (1008 bp) from Pisum sativum, and purification of all the encoded recombinant proteins (Ga, 44 kDa; Gb, 41 kDa; Gc, 14 kDa; GPCR, 35 kDa). The transcript levels of Ga and Gb were upregulated following NaCl, heat and H 2 O 2 treatments. Protein-protein interaction studies using an in vitro yeast two-hybrid system and in planta co-immunoprecipitation showed that the Ga subunit interacted with the pea Gb subunit and pea phospholipase C (PLCd) at the calcium-binding domain (C2). The GTPase activity of the Ga subunit increased after interaction with PLCd. The GPCR protein interacted with all the subunits of G-proteins and with itself. Transgenic tobacco plants (T 0 and T 1 ) constitutively over-expressing Ga showed tolerance to salinity and heat, while Gb-over-expressing plants showed only heat tolerance, as tested by leaf disk senescence assay and germination/growth of T 1 seeds/seedlings. These findings provide direct evidence for a novel role of Ga and Gb subunits in abiotic stress tolerance and possible cross-talk between PLC-and G-protein-mediated signaling pathways.

Bloom's syndrome (BS) and Fanconi anemia (FA) are autosomal recessive disorders characterized by cancer and chromosomal instability. BS and FA group J arise from mutations in the BLM and FANCJ genes, respectively, which encode DNA helicases. In this work, FANCJ and BLM were found to interact physically and functionally in human cells and co-localize to nuclear foci in response to replication stress. The cellular level of BLM is strongly dependent upon FANCJ, and BLM is degraded by a proteasome-mediated pathway when FANCJ is depleted. FANCJdeficient cells display increased sister chromatid exchange and sensitivity to replication stress. Expression of a FANCJ C-terminal fragment that interacts with BLM exerted a dominant negative effect on hydroxyurea resistance by interfering with the FANCJ-BLM interaction. FANCJ and BLM synergistically unwound a DNA duplex substrate with sugar phosphate backbone discontinuity, but not an 'undamaged' duplex. Collectively, the results suggest that FANCJ catalytic activity and its effect on BLM protein stability contribute to preservation of genomic stability and a normal response to replication stress.

Conserved Iron–Sulfur (Fe–S) clusters are found in a growing family of metalloproteins that are implicated in prokaryotic and eukaryotic DNA replication and repair. Among these are DNA helicase and helicase–nuclease enzymes that preserve chromosomal stability and are genetically linked to diseases characterized by DNA repair defects and/or a poor response to replication stress. Insight to the structural and functional importance of the conserved Fe–S domain in DNA helicases has been gleaned from structural studies of the purified proteins and characterization of Fe–S cluster site-directed mutants. In this review, we will provide a current perspective of what is known about the Fe–S cluster helicases, with an emphasis on how the conserved redox active domain may facilitate mechanistic aspects of helicase function. We will discuss testable models for how the conserved Fe–S cluster might operate in helicase and helicase–nuclease enzymes to conduct their specialized functions that help to preserve the integrity of the genome.