Fanconi anaemia (FA) is a chromosomal instability disorder characterized by cellular sensitivity to DNA interstrand crosslinking agents and a high risk of cancer. Six of the eight proteins encoded by the known FA genes form a nuclear complex which is required for the monoubiquitination of the FANCD2 protein. FANCD2 complexes and colocalizes with BRCA1, but its presumptive role in DNA repair has not yet been clearly defined. We used yeast two-hybrid analysis to test for interaction between FANCD2 and 10 proteins involved in homologous recombination repair. FANCD2 did not interact with RAD51, the five RAD51 paralogs, RAD52, RAD54 or DMC1. However, it bound to a highly conserved C-terminal site in BRCA2 that also binds FANCG/XRCC9. FANCD2 and BRCA2 can be coimmunoprecipitated from cell extracts of both human and Chinese hamster wild-type cells, thus confirming that the interaction occurs in vivo. Formation of nuclear foci of FANCD2 was normal in the BRCA2 mutant CAPAN-1 cells, which indicates that the recruitment of FANCD2 to sites of DNA-repair is independent of wild-type BRCA2 function. FANCD2 colocalized with RAD51 in foci following treatment with mitomycin C or hydroxyurea, and colocalized very tightly with PCNA after treatment with hydroxyurea. These findings suggest that FANCD2 may have a role in the cellular response to stalled replication forks or in the repair of replication-associated double-strand breaks, irrespective of the type of primary DNA lesion.

Previous work has shown several proteins defective in Fanconi anemia (FA) are phosphorylated in a functionally critical manner. FANCA is phosphorylated after DNA damage and localized to chromatin, but the site and significance of this phosphorylation are unknown. Mass spectrometry of FANCA revealed one phosphopeptide, phosphorylated on serine 1449. Serine 1449 phosphorylation was induced after DNA damage but not during S phase, in contrast to other posttranslational modifications of FA proteins. Furthermore, the S1449A mutant failed to completely correct a variety of FA-associated phenotypes. The DNA damage response is coordinated by phosphorylation events initiated by apical kinases ATM (ataxia telangectasia mutated) and ATR (ATM and Rad3-related), and ATR is essential for proper FA pathway function. Serine 1449 is in a consensus ATM/ATR site, phosphorylation in vivo is dependent on ATR, and ATR phosphorylated FANCA on serine 1449 in vitro. Phosphorylation of FANCA on serine 1449 is a DNA damage-specific event that is downstream of ATR and is functionally important in the FA pathway.

For finite p-groups P of class 2 and exponent p the following are invariants of fully refined central decompositions of P : the number of members in the decomposition, the multiset of orders of the members, and the multiset of orders of their centers. Unlike for direct product decompositions, Aut P is not always transitive on the set of fully refined central decompositions, and the number of orbits can in fact be any positive integer. The proofs use the standard semi-simple and radical structure of Jordan rings. These rings also produce useful criteria for a p-group to be centrally indecomposable. Applications to p-groups of class 2 and arbitrary exponent are also provided.

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For a range of eukaryote transcripts, the initiation of degradation is coincident with the addition of a short pyrimidine tag at the 3= end. Previously, cytoplasmic mRNA tagging has been observed for human and fungal transcripts. We now report that Arabidopsis thaliana mRNA is subject to 3= tagging with U and C nucleotides, as in Aspergillus nidulans. Mutations that disrupt tagging, including A. nidulans cutA and a newly characterized gene, cutB, retard transcript degradation. Importantly, nonsensemediated decay (NMD), a major checkpoint for transcript fidelity, elicits 3= tagging of transcripts containing a premature termination codon (PTC). Although PTC-induced transcript degradation does not require 3= tagging, subsequent dissociation of mRNA from ribosomes is retarded in tagging mutants. Additionally, tagging of wild-type and NMD-inducing transcripts is greatly reduced in strains lacking Upf1, a conserved NMD factor also required for human histone mRNA tagging. We argue that PTC-induced translational termination differs fundamentally from normal termination in polyadenylated transcripts, as it leads to transcript degradation and prevents rather than facilitates further translation. Furthermore, transcript deadenylation and the consequent dissociation of poly(A) binding protein will result in PTC-like termination events which recruit Upf1, resulting in mRNA 3= tagging, ribosome clearance, and transcript degradation. Modulation of mRNA function within the cytoplasm is critical to the control of gene expression, function being determined primarily by the balance between transcript degradation and translation. Two cotranscriptional modifications, the 5= cap and the 3= poly(A) tail, are essential to both mRNA transcript stability and translation (15,81,83), and integral to this is their association mediated by an array of proteins which modulate function (6, 71).The poly(A) tail, a homopolymeric sequence at the 3= end of transcripts, is added by the canonical poly(A) polymerase in the nucleus. Within the cytoplasm, controlled deadenylation of this tail to ϳA15 in fungi and ϳA15 to A25 in mammals generally precedes decapping and subsequent 5=-3= and/or exosome-dependent 3=-5= decay (17,20,60,64,66). In specific instances, e.g., during embryonic development, deadenylated transcripts remain translationally dormant and can be reactivated by cytoplasmic adenylation (45). Deadenylation is a key control point through which rapid physiological change can occur. However, the mechanisms that underlie this switch between translation and mRNA turnover remain poorly understood.It has recently been discovered that poly(A) tails in Aspergillus nidulans and Schizosaccharomyces pombe are modified in the cytoplasm with the addition of nontemplated U or C/U-rich tags at the point of mRNA decapping, and this increases the rate of transcript degradation (60, 76). Human H2a and H3.3 mRNAs, which are not polyadenylated, also undergo 3= uridylation prior to decapping and degradation (67). This 3= tagging of mRNA is conducted by noncanon...

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Fanconi Anemia (FA) is a cancer-prone inherited bone marrow failure and cancer susceptibility syndrome with at least 13 complementation groups (FANCA, -B, -C, -D1, -D2, -E,-F, -G, -I, -J, -L, -M, -N). Our laboratory has previously described several regulatory phosphorylation events for core complex member proteins FANCG and FANCA by phosphorylation. In this study we report a novel phosphorylation site S331 of FANCD2, the pivotal downstream player of the FA pathway. Phosphorylation of S331 is important for its DNA damage inducible monoubiquitylation, resistance to DNA crosslinkers and in vivo interaction with FANCD1/BRCA2. A phosphomimetic mutation at S331 restores all of these phenotypes to wild type. In vitro and in vivo experiments show phosphorylation of S331 is mediated by CHK1, the S phase checkpoint kinase implicated in the FA DNA repair pathway.