Microtubule-associated protein MAP2 preferentially binds to a dA/dT sequence present in mouse satellite DNA

Microtubule-associated protein MAP2 binds to the Sau96.1 restriction monomer fragment of mouse satellite DNA. This fragment is also present in a lower proportion in bulk DNA. The digestion of MAP2-Sau96.1 fragment complex by DNase results in the protection of certain nucleotide sequences. The sequence poly(dA)4/poly(dT)4 is mainly protected against DNase digestion.     

High-frequency conversion to a "fluffy" developmental phenotype in Aspergillus spp. by 5-azacytidine treatment: evidence for involvement of a single nuclear gene.

Transient exposure of mycelia from Aspergillus niger and Aspergillus nidulans to the cytidine analog 5-azacytidine, leading to no more than 0.3 to 0.5% substitution for cytosine by 5-azacytosine in A. nidulans DNA, resulted in the conversion of a high fraction of the cell population (more than 20%) to a mitotically and meiotically stable "fluffy" developmental phenotype. The phenotypic variants are characterized by the developmentally timed production of a profuse fluffy network of undifferentiated aerial hyphae that seem to escape signals governing vegetative growth. Genetic analysis with six different fluffy clones reveals that this trait is not cytoplasmically coded, is recessive in heterozygous diploids but codominant in heterokaryons, and exhibits a 1:1 Mendelian segregation pattern upon sexual sporulation of heterozygous diploids. Complementation and mitotic haploidization studies indicated that all variants are affected in the same gene, which can be tentatively located on chromosome VIII of A. nidulans. Molecular analysis to search for modified bases showed that DNA methylation is negligible in in both A. niger and A. nidulans and that no differences could be detected among DNAs from wild-type cells, fluffy clones, or mycelia exposed to 5-azacytidine. It thus appears that high-frequency conversion of fungal mycelia to a stable, variant developmental phenotype by 5-azacytidine is the result of some kind of target action on a single nuclear gene and that this conversion can occur in organisms virtually devoid of DNA methylation.     

Electron microscopy of thin sections of Candida utilis: The structure of the cell wall

Summary Details of the structure of the Candida utilis cell wall were described. Using intact cells, cell walls, about 0.02 m thick, have been resolved into three electron dense layers, each about 700 Å thick, made up of materials of very similar electron opacity. The central and the inner layers of the wall seem to be closely packed forming a slightly more compact structure of somewhat greater electron density. Laminations were observed in some of the inner layers of the sections, particularly in some areas where the cell wall had separated: The possibility of this lamination being associated with the presence of chitin in the framework of the cell wall is discussed. Interesting observations have also been made in the sections of the heat-killed cells confirming the existence of a central electron dense cell wall layer, differing from the inner and the outer ones. Underlying the cell wall is the cytoplasmic membrane, a not too well defined sinous structure with some invaginations.     

Structure-function relationships in heparin cofactor II: chemical modification of arginine and tryptophan and demonstration of a two-domain structure

Heparin cofactor II and antithrombin III are plasma proteins functionally similar in their ability to inhibit thrombin at accelerated rates in the presence of heparin. To further characterize the structural and functional properties of human heparin cofactor II as compared to antithrombin III, we studied the possible significance of arginyl and tryptophanyl residues and the changes in protein structure and activity during guanidinium chloride (GdmCl) denaturation. Both antithrombin and heparin cofactor activities of heparin cofactor II are inactivated by the arginine-specific reagent, 2,3-butanedione. Saturation kinetics are observed during modification and suggest formation of a reversible protease inhibitor-butanedione complex. Quantitation of arginyl residues following butanedione modification shows a loss of about four residues for total inactivation, one of which is essential for antithrombin activity. Arginine-modified heparin cofactor II did not bind to heparin-agarose and implies a role for the other modified arginyl residues during heparin cofactor activity. N-Bromosuccinimide oxidation (20 mol of reagent/mol of protein) of heparin cofactor II results in modification of approximately two tryptophanyl residues with no concomitant loss of heparin cofactor activity. Moreover, there is no enhancement of intrinsic protein fluorescence during heparin binding to the native inhibitor. Circular dichroism measurements show that the structural transition of heparin cofactor II during denaturation is distinctly biphasic, yielding midpoints at 0.6 and 2.6 M GdmCl. Functional protease inhibitory activities are affected to the same extent following denaturation-renaturation at various GdmCl concentrations. The results indicate that arginyl residues are critical for both antithrombin and heparin binding activities. In contrast, tryptophanyl residues are apparently not essential for heparin-dependent interactions. The results also suggest that heparin cofactor II contains two structural domains which unfold at different GdmCl concentrations.     

Abiotic influences on embryo growth: statoliths as experimental tools in the squid early life history

Statolith size and growth was used to determine the influence of abiotic factors on the growth of Loligo vulgaris and Sepioteuthis australis embryos. Recently spawned egg masses collected from the field were incubated in the laboratory under different levels of light intensity, photoperiod, or short periods of low salinity (30‰). Double tetracycline staining was used to follow statolith growth. In L. vulgaris constant light conditions produced significantly slower growth in the embryonic statoliths and embryos held at summer photoperiod had slower statolith growth than those held at winter photoperiods. However once they hatched out there was no evidence that photoperiod affected statolith growth. After hatching, in all photoperiods statolith growth rates decreased in comparison with late embryonic rates. In S. australis embryos, differences between the high and medium light intensities for summer and intermediate photoperiods were found, suggesting that under summer incubation temperature, longer daylengths at medium light intensity favoured higher statolith growth for this species. In comparison to controls, slower statolith growth in S. australis embryos due to low salinity only occurred when exposed for 72 h. Comparison with previous studies indicates that temperature seems to be the main abiotic factor influencing statolith growth during early stages, however, interactions among all abiotic factors needs to be determined as well as the unknown influence of other isolated factors, e.g., oxygen concentration within the egg mass.     

Decrease of phosphofructokinase activity in relation to the pathogenesis of triorthocresyl-phosphate-induced delayed neuropathy.

The in vivo effect of a single dose of the neuropathic compound triorthocresyl-phosphate (TOCP) on phosphofructokinase (PFC, E.C. 2.7.1.11) and its relation with the initiation step (inhibition and aging of neuropathy target esterase, NTE) in the TOCP-induced delayed neuropathy have been studied. Hens were treated with a neurotoxic dose of TOCP (500 mg/kg, p.o.) and with a protective compound (Phenylmethanesulfonyl fluoride, PMSF, 30 mg/kg s.c.) in different combinations: TOCP, TOCP + PMSF, PMSF + TOCP and PMSF. PFK activity was determined in brain and sciatic nerve 1, 3, 7 and 15 days after treatment. PFK activity decreased in sciatic nerve 15 days after dosing with TOCP or TOCP + PMSF. When animals were dosed with the protective agent (PMSF) alone or before administering the neurotoxic compound, PFK activity was unaltered and clinical signs of neuropathy were absent. The data presented here suggest that phosphofructokinase is involved in the pathogenesis of the neuropathy induced by TOCP.     

Human platelet arginase

Summary We report here, for the first time the presence of arginase in human platelets. This enzyme has been partially purified and some of its properties studied. Its biological significance and its involvement in polyamine biosynthesis are considered.