Purification and characterization of delta helicase from fetal calf thymus.

A DNA helicase (delta helicase) which partially copurifies with DNA polymerase delta has been highly purified from fetal calf thymus. delta helicase differs in physical and enzymatic properties from other eukaryotic DNA helicases described thus far. The enzyme has an apparent mass of 57 kDa by gel filtration and is associated with polypeptides of 56 and 52 kDa by SDS-polyacrylamide gel electrophoresis. Photo-cross-linking of the purified enzyme with [alpha-32P]ATP resulted in labeling of a polypeptide of approximately 58 kDa, suggesting that the active site is present on the larger polypeptide. Unwinding of a partial duplex requires a nucleoside triphosphate which can be either ATP or dATP but not a nonhydrolyzable analogue of ATP. Other ribo- and deoxyribonucleoside triphosphates have little or no activity as cofactors. delta helicase also has DNA-dependent ATPase activity which has a relatively low Km for ATP (40 microM). delta helicase binds to single-stranded DNA but has little or no affinity for double-stranded DNA or single-stranded RNA. Similar to replicative DNA helicases from prokaryotes and the herpes simplex virus type 1 helicase-primase, delta helicase translocates in the 5'-3' direction along the strand to which it is bound and preferentially unwinds DNA substrates with a forklike structure.     

Inhibition of xanthine oxidase by uric acid and its influence on superoxide radical production.

The inhibition of xanthine oxidase by its reaction product, uric acid, was studied by steady state kinetic analysis. Uric acid behaved as an uncompetitive inhibitor of xanthine oxidase with respect to the reducing substrate, xanthine. Under 50 microM xanthine and 210 microM oxygen, the apparent K(i) for uric acid was 70 microM. Uric acid-mediated xanthine oxidase inhibition also caused an increase in the percentage of univalent reoxidation of the enzyme (superoxide radical production). Steady-state rate equations derived by the King-Altman method support the formation of an abortive-inhibitory enzyme-uric acid complex (dead-end product inhibition). Alternatively, inhibition could also depend on the reversibility of the classical ping-pong mechanism present in xanthine oxidase-catalyzed reactions.     

Growth effects of nagilactone E on cultured cells of lettuce

Nagilactone E, a norditerpene dilactone isolated from a gymnosperm, Podocarpus nagi (Podocarpaceae), was able to stimulate the growth of cultured cells of Lactuca sativa cv. Grand Rapids at 0.1 g ml^-1 but not at 0.01 or 1 g ml^-1. Cell wet weight/unit time and cell number/unit wet weight were increased when they were recorded at the end of the 14-day incubation period. Also, the population of cells treated with that concentration of nagilactone E had a higher percentage of cells with shorter cell length compared to the control (untreated).     

Preliminary study of the distribution of the toxic elements As,Cd, and Hg in human hair and tissues by RNAA

In order to study the relationships between trace element concentrations of hair and internal body burdens, a radiochemical NAA technique has been used for determination of the elements As, Cd, and Hg in autopsy samples of liver, kidney-cortex, lung, and hair from 24 male persons who died by accident. High significant positive correlations were observed between the As concentration in hair and in kidney-cortex, and between Cd and Zn concentrations in kidney-cortex. The contents of Cd, both for lung and kidney-cortex, were related to the smoking habits of the subjects.

     

A modular domain of NifU,a nitrogen fixation cluster protein,is highly conserved in evolution

HnifU, a gene exhibiting similarity tonifU genes of nitrogen fixation gene clusters, was identified in the course of expressed sequence tag (EST) generation from a human fetal heart cDNA library. Northern blot of human tissues and polymerase chain reaction (PCR) using human genomic DNA verified that the hnifU gene represented a human gene rather than a microbial contaminant of the cDNA library. Conceptual translation of the hnifU cDNA yielded a protein product bearing 77% and 70% amino acid identity to NifU-like hypothetical proteins fromHaemophilus influenzae andSaccharomyces cerevisiae, respectively, and 40–44% identity to the N-terminal regions of NifU proteins from several diazatrophs (i.e., nitrogen-fixing organisms). Pairwise determination of amino acid identities between the NifU-like proteins of nondiazatrophs showed that these NifU-like proteins exhibited higher sequence identity to each other (63–77%) than to the diazatrophic NifU proteins (40–48%). Further, the NifU-like proteins of non-nitrogenfixing organisms were similar only to the N-terminal region of diazatrophic NifU proteins and therefore identified a novel modular domain in these NifU proteins. These findings support the hypothesis that NifU is indeed a modular protein. The high degree of sequence similarity between NifU-like proteins from species as divergent as humans andH. influenzae suggests that these proteins perform some basic cellular function and may be among the most highly conserved proteins. Correspondence to: C.-C. Liew     

中国单头螨属一新种(蜱螨亚纲：叶螨科)

中国单头螨属一新种（蜱螨亚纲：叶螨科）谭瑞成,鲁素玲（湖南省林业科学研究所长沙４１０００４）（新疆石河子农学院新疆８３２００３）单头螨属ＡｐｌｏｎｏｂｉａＷＯｍｅｒｓｌｅｙ,１９４０前足体背毛３对,后半体背毛１０对,全部或部分背毛着生在明显结节Ｌ,背...     

Translational control of programmed cell death: eukaryotic translation initiation factor 4E blocks apoptosis in growth-factor-restricted fibroblasts with physiologically expressed or deregulated Myc.

There is increasing evidence that cell cycle transit is potentially lethal, with survival depending on the activation of metabolic pathways which block apoptosis. However, the identities of those pathways coupling cell cycle transit to survival remain undefined. Here we show that the eukaryotic translation initiation factor 4E (eIF4E) can mediate both proliferative and survival signaling. Overexpression of eIF4E completely substituted for serum or individual growth factors in preserving the viability of established NIH 3T3 fibroblasts. An eIF4E mutant (Ser-53 changed to Ala) defective in mediating its growth-factor-regulated functions was also defective in its survival signaling. Survival signaling by enforced expression of eIF4E did not result from autocrine release of survival factors, nor did it lead to increased expression of the apoptosis antagonists Bcl-2 and Bcl-XL. In addition, the execution apparatus of the apoptotic response in eIF4E-overexpressing cells was found to be intact. Increased expression of eIF4E was sufficient to inhibit apoptosis in serum-restricted primary fibroblasts with enforced expression of Myc. In contrast, activation of Ha-Ras, which is required for eIF4E proliferative signaling, did not suppress Myc-induced apoptosis. These data suggest that the eIF4E-activated pathways leading to survival and cell cycle progression are distinct. This dual signaling of proliferation and survival might be the basis for the potency of eIF4E as an inducer of neoplastic transformation.     

Glycine substitutions in the triple-helical region of type VII collagen result in a spectrum of dystrophic epidermolysis bullosa phenotypes and patterns of inheritance.

The dystrophic forms of epidermolysis bullosa (DEB) are characterized by fragility of the skin and mucous membranes. DEB can be inherited in either an autosomal dominant or autosomal recessive pattern, and the spectrum of clinical severity is highly variable. The unifying diagnostic hallmark of DEB is abnormalities in the anchoring fibrils, which consist of type VII collagen, and, recently, mutations in the corresponding gene, COL7A1, have been disclosed in a number of families. In this study, we report six families with glycine substitution mutations in the triple-helical region of type VII collagen. Among the six families, two demonstrated a mild phenotype, and the inheritance of the mutation was consistent with the dominantly inherited form of DEB. In the four other families, the mutation was silent in the heterozygous state but, when present in the homozygous state, or combined with a second mutation, resulted in a recessively inherited DEB phenotype. Type VII collagen is, therefore, unique among the collagen genes, in that different glycine substitutions can be either silent in heterozygous individuals or result in a dominantly inherited DEB. Inspection of the locations of the glycine substitutions along the COL7A1 polypeptide suggests that the consequences of these mutations, in terms of phenotype and pattern of inheritance, are position independent.     

Ribotyping to differentiate Fusobacterium necrophorum subsp. necrophorum and F. necrophorum subsp. funduliforme isolated from bovine ruminal contents and liver abscesses.

Differences in biological activities (hemagglutination, hemolytic, leukotoxic, and virulence) and ribotypes between the two subspecies of Fusobacterium necrophorum of bovine ruminal and liver abscess origins were investigated. Hemagglutination activity was present in all hepatic, but only some ruminal, strains of Fusobacterium necrophorum subsp. necrophorum. Ruminal F. necrophorum subsp. necrophorum had low leukotoxin titers yet was virulent in mice. Fusobacterium necrophorum subsp. funduliforme of hepatic or ruminal origin had no hemagglutination activity, had low hemolytic and leukotoxic activities, and was less virulent to mice. For ribotyping, chromosomal DNAs of 10 F. necrophorum subsp. necrophorum and 11 F. necrophorum subsp. funduliforme isolates were digested with restriction endonucleases (EcoRI, EcoRV, SalI, PstI, and HaeIII) and examined by restriction fragment length polymorphisms after hybridizing with a digoxigenin-labeled cDNA probe transcribed from a mixture of 16 and 23S rRNAs from Escherichia coli. The most discriminating restriction endonuclease enzyme for ribotyping was EcoRI. The presence or absence of two distinct bands of 2.6 and 4.3 kb differentiated the two subspecies. Regardless of the origin, only F. necrophorum subsp. necrophorum, a virulent subspecies, had a ca. 2.6-kb band, whereas F. necrophorum subsp. funduliforme, a less virulent subspecies, had a ca. 4.3-kb band. Ribotyping appears to be a useful technique to genetically differentiate the two subspecies of F. necrophorum.