Seventh International Workshop on Ataxia-Telangiectasia

Ataxia-telangiectasia (A-T) is a rare hereditary syndrome involving cerebellar degeneration, immunodeficiency, cancer risk, and radiosensitivity. Since the cloning of the A-T gene, ATM, in 1995, research on this pleiotropic disease and its molecular basis has expanded tremendously. ATM is a large protein kinase that appears to be one of the primary sensors of DNA strand-break damage. The vast majority of mutations in ATM result in truncation and destabilization of the protein, but certain missense and splicing errors have been shown to result in a less severe phenotype. A-T heterozygotes have been shown to have a slightly increased risk of cancer, but their increased in vitro radiosensitivity does not seem to result in any in vivo sensitivity. ATM does seem to act as a classic tumor suppressor gene in T-prolymphocytic leukemia, and LOH at the ATM locus is a common event in some tumor types, suggesting a general role for ATM in cancer. Recent work has shown the interaction of ATM with proteins involved in cell cycle control, and the direct phosphorylation of some of these interactors by ATM. ATM knockout mice have been created by several groups, and recapitulate the immunodeficiency, radiosensitivity, cancer risk, and fertility defects of A-T, although the effect on the cerebellum is slight. These diverse topics, and their integration into a global understanding of A-T, were the basis of the 7th International A-T Workshop.     

Structure-function analysis of the herpes simplex virus type 1 UL12 gene: correlation of deoxyribonuclease activity in vitro with replication function

Although the product of the UL12 gene of herpes simplex virus type 1 (HSV-1) has been shown to possess both exonuclease and endonuclease activities in vitro, and deletion of most of the gene within the viral genome results in inefficient production and maturation of infectious virions, the function of the deoxyribonuclease (DNase) activity per se in virus replication remains unclear. In order to correlate the in vitro and in vivo activities of the protein encoded by UL12, mutant proteins were tested for nuclease activity in vitro by a novel hypersensitivity cleavage assay and for their ability to complement the replication of a DNase null mutant, AN-1. Rabbit reticulocyte lysates programmed with wild-type UL12 RNA cleaved at the same sites cleaved by purified HSV-1 DNase, but distinct from those cleaved by DNase 1 or micrococcal nuclease. All mutants which lacked DNase activity in vitro also failed to complement the replication of AN-1 in nonpermissive cells. Likewise, all mutants which contained HSV-1 DNase activity, as detected by the hypersensitivity cleavage assay, were capable of complementing the replication of the DNase null mutant, though to varying extents. Of particular note was the d1-126 mutant protein, which, despite having the same specific activity as the wild-type enzyme in vitro, complemented the replication of AN-1 significantly less than the wild-type protein. The results suggest that DNase activity per se is required for efficient replication of HSV-1 in vivo. However, residues, including the N-terminal 126 amino acids, which are dispensable for enzymatic activity in vitro may facilitate the accessibility or activity of the protein in vivo.     

Mental status and fragile X expression in relation to FMR-1 gene mutation

The fragile X mental retardation syndrome is caused by unstable expansion of a CGG repeat in the FMR-1 gene. Clinical expression is associated with a large expansion of the CGG repeat. The mutation in the FMR-1 gene and the cytogenetic expression of the fragile site at Xq27.3 have been studied in 52 fragile X male patients. The percentage of the cytogenetic expression of the fragile site at Xq27.3 positively correlates with the mean size of the full mutation in the FMR-1 gene (p < 0.0001) irrespective of the presence of additional premutation alleles. We noted a less frequent occurrence of additional premutation alleles in adult patients compared with juveniles, suggesting a continued mitotic instability in life. Additionally, the level of mental retardation has been ascertained in 35 patients using the Stanford-Binet or Terman-Merrill test of general intelligence. The presence of a full mutation in the FMR-1 gene seemed decisive for the occurrence of mental impairment in the patient. No correlation is observed between the degree of mental retardation and the size of the full mutation. The degree of mental retardation seemed not to be influenced by the presence of premutation alleles in part of the cells in addition to a full mutation. One patient is described with the 'Prader-Willi-like' subphenotype of the fragile X syndrome, showing a deletion in the FMR-1 gene in a part of his cells in addition to a full mutation.     

The crystallographic structure of the protease from human immunodeficiency virus type 2 with two synthetic peptidic transition state analog inhibitors

The crystal structure of human immunodeficiency virus (HIV) type 2 protease has been determined in complexes with peptidic inhibitors Noa-His-Cha psi [CH(OH)CH(OH)]Val-Ile-Amp (U75875) and Qnc-Asn-Cha psi [CH(OH)CH2]Val-Npt(U92163) (where Noa is naphthyloxyacetyl, Cha is cyclohexylalanine, Amp is 2-aminomethylpyridine, Qnc is quinoline-2-carbonyl, and Npt is neopentylamine), which have dihydroxyethylene and hydroxyethylene moieties, respectively, in place of the normal scissile bond of the natural ligand. The complexes crystallize in space group P2(1)2(1)2(1), with one dimer-inhibitor complex per asymmetric unit and average cell dimensions of a = 33.28 A, b = 45.35 A, c = 135.84 A. Data were collected to approximately 2.5-A resolution. The model structures were refined with resulting R-factors of around 0.19. As expected, the HIV-2 protease structure is approximately C2-symmetric with a gross structure very similar to that of the HIV-1 enzyme. The inhibitors bind in an extended conformation positioned lengthwise in the binding cleft in a manner similar to that found in the HIV-1 protease-inhibitor complexes previously reported. The substitution of the bulkier Ile82 side chain in the HIV-2 protease may help explain the better ability of HIV-2 protease to bind and hydrolyze ligands with small P1 and P1' side groups. It appears that differences in specificity between the proteases of HIV-1 and HIV-2 are not merely a result of simple side chain substitutions, but may be complicated by differences in main chain flexibility as well.     

Dietary risk factors for pre-eclampsia among women attending Harare Maternity Hospital, Zimbabwe

OBJECTIVE: To identify specific foods that predispose Zimbabwean women to a higher or lower risk of pre-eclampsia and/or eclampsia. DESIGN: A case control study was implemented. Participants were asked by questionnaire to recall the specific amounts of meats, poultry, fruits, fish, vegetables and dairy products they had consumed in the month prior to giving birth. SETTING: Harare Maternity Hospital, Harare, Zimbabwe between June of 1995 and April of 1996. SUBJECTS: 180 women clinically diagnosed with pre-eclampsia (144) or eclampsia (36), and 194 normotensive women without these conditions. MAIN OUTCOME MEASURES: Pre-eclampsia/eclampsia. RESULTS: There were few associations between consumption of specific food items and the occurrence of pre-eclampsia/eclampsia. Meat and fruit were the only foods found to be significantly associated with pre-eclampsia. Women who consumed 12 or more servings of meat per month were more likely to have pre-eclampsia/eclampsia when compared to women eating 11 servings of meat or less per month. While intake of bananas and mangos was unrelated to risk, women who consumed other fruits (i.e. apples, oranges, grapes, peaches, apricots, paw paw, and plums), were 1.7 (95% CI = 1.0 to 3.1) times more likely to develop pre-eclampsia/eclampsia as women who ate none of these fruits. However, women who consumed relatively large quantities of these fruits were not at a particularly high risk. Increased consumption of kapenta was modestly associated with a decrease in disease risk, but this finding was well within the limits of chance and no association was present with intake of other types of fish. CONCLUSIONS: Our findings suggest that variation in consumption of specific foods do not have a strong effect on the incidence of pre-eclampsia in this population. However, further research involving the use of a more comprehensive dietary measure, biochemical measurements of nutrients, pre-pregnancy assessment and ascertainment of dietary intake prior to the development of pre-eclampsia are needed.