Israel Medical Association Journal

We describe a unique E3, the F-box protein, Ufo1, of yeast. Ufo1 recruits the mating switch endonuclease, Ho, to the SCF complex for ubiquitylation. In addition to the F-box and WD40 protein-protein interaction domains found in all F-box proteins, Ufo1 has a unique domain comprising multiple copies of the ubiquitin-interacting motif. Ufo1 interacts with the UbL-UbA protein, Ddi1, via its UIMs[1], and this is required for turnover of SCF ^Ufo1 complexes. This is a novel function for an UbL-UbA protein. Deletion of the genomic UFO1 UIMs is lethal and our data indicate that Ufo1ΔUIM acts as a dominant negative leading to inhibition of the SCF pathway of substrate degradation and to cell cycle arrest. Furthermore, we found that Ddi1 is required for the final stages of degradation of Ho endonuclease. In the absence of Ddi1, Ho does not form a complex with the 19S RP and is stabilized. Stabilization of Ho leads to perturbation of the cell cycle and to the formation of multi-budded cells. Our experiments uncover a novel role for the ubiquitin-proteasome system in maintenance of genome stability.

Background: Primary pulmonary hypertension is a rare disorder, characterized by progressive pulmonary hypertension and right heart failure. It may be familial or sporadic. Mutations in bone morphogenetic protein receptor II (BMPR2), a member of the transforming growth factor-beta receptor superfamily of receptors, underlie many cases of the disorder.

Objectives: To perform molecular analysis of a patient with familial PPH[1] and provide her and her family with suitable genetic counseling.

Methods: DNA was extracted from 10 ml whole blood, and the BMPR2 gene was screened for mutations. Individual exons were amplified by polymerase chain reaction and sequenced. Mutation confirmation and molecular characterization of additional family members was performed using restriction enzyme analysis followed by appropriate genetic counseling.

Results: We identified a novel T to C missense mutation expected to result in substitution of arginine for a conserved cysteine in the ligand-binding domain of BMPR2. Screening of family members demonstrated the presence of the mutation in the father and a younger asymptomatic sister of the index patient.

Conclusions: Molecular diagnosis in PPH allows for identification of at-risk family members and raises the option of earlier diagnosis and possibly instituting earlier treatment in affected individuals. However, molecular screening of asymptomatic family members raises difficult ethical questions that can only be resolved by conducting large multicenter prospective studies in BMPR2 carriers.

Fanconi anemia is a rare autosomal recessive disorder characterized clinically by congenital abnormalities, progressive bone marrow failure, and a predisposition to malignancy. FA cells are sensitive to DNA cross-linking agents. Complementation analysis of FA cells using somatic cell fusion has facilitated the identification of eight complementation groups, suggesting that FA is a genetically heterogeneous disorder. Six genes (FANCA, FANCC, FANCD2, FANCE, FANGF, FANCG) have been cloned so far. The majority of affected patients belong to FA group A. Of the 32 unrelated Israeli patients with FA that we studied, 6 carried the FANCC mutations and 15 the FANCA mutations. Among the Jewish patients, ethnic-related mutations were common. Recent cumulative evidence suggests that the FA proteins are repair proteins. FANCC, FANCA and FANCG bind and interact in a protein complex found in the cytoplasm and nucleus of normal cells. FANCD2 exists in two isoforms; the long active form, FANCD2-L, is absent from FA cells of all complementation groups. FANCD2 co-localized with BRCA1 in unclear foci, probably as part of a large genomic surveillance complex. Studies using FANCA and FANCC knockout mice suggest that bone marrow precursors express interferon-g hypersensitivity and show progressive apoptosis. The definition of the molecular basis of FA in many affected families now enables prenatal diagnosis.