The base analog 6-N-hydroxylaminopurine (HAP) mutagenesis is dependent on the integrity of the uvsE, uvsF and uvsB genes in Aspergillus nidulans

Most of the available data in lower eukaryotes are consistent with the idea that base analogs-induced mutagenesis is due to the mis-pairing properties of these compounds, which, in turn, is due to a shift in the tautomeric equilibrium of the molecule. A tautomeric shift may in fact lead to mismatches which, at least in Escherichia coli, can be repaired by genes involved in the post-replicative mismatch repair whose activity is necessary to control spontaneous mutagenesis. In filamentous fungi, such as Aspergillus nidulans, nothing is known about the repair of base pairing mistakes after base analogs treatment. For this reason, we have decided to screen UV-sensitive Aspergillus nidulans mutants for their mutagenic response to 6-N-hydroxylaminopurine (HAP). We have shown that three mutations (uvsB, uvsC and uvsE), which enhance the UV-sensitivity of germinating conidia, cause a lower mutagenic response to HAP. On the other hand, the uvsH mutation, has no effect on HAP-induced mutagenesis.     

Prenylated anthranoids from Psorospermum species

The chemical composition of the root extracts of two Psorospermum sp. from the Ivory Coast is reported. Together with previously known compounds, acetylvismione F and 2-geranylemodin anthrone were isolated from P. corymbiferum, and vismione G from P. glaberrimum. Geranyl substitution is confirmed to be a typical feature of this genus.     

7,2′,4′-Trihydroxy-3′-methoxyisoflavone from zollernia paraensis

Three further compounds have been isolated from Zollernia paraensis: 2,7-dihydroxy-4′-methoxy-3-phenylcoumarin, (±)-5,7-dihydroxy-2′,4′-dimethoxyisoflavanone and the new 7,2′,4′-trihydroxy-3′-methoxyisoflavone.     

Wild birds as hosts of Amblyomma cajennense (Fabricius, 1787) (Acari: Ixodidae).

We evaluated the prevalence, mean intensity and relative density of ticks in 467 wild birds of 67 species (12 families) from forest and cerrado habitats at two protected areas of Minas Gerais, between March and September 1997. Ticks collected (n=177) were identified as larvae and nymphs of Amblyomma cajennense and four other species of Amblyomma. We report for the first time 28 bird species as hosts of the immature stages of A. cajennense, demonstrating the lack of host specificity of the larvae and nymphs. A. cajennense had 15% prevalence on birds, with a mean infestation intensity of 0.37 ticks per host sampled, and 2.5 ticks per infested bird. Prevalence varied in relation to host species, diet and between birds from forests at two successional stages. There were no differences in relation to host forest dependence, participation in mixed flocks of birds, and nest type constructed. A. cajennense is a species of medical and veterinary importance, occurring on domestic animals but is known little of its occurrence on wildlife.     

In vivo N-glycosylation of the mep2 high-affinity ammonium transporter of Saccharomyces cerevisiae reveals an extracytosolic N-terminus

Saccharomyces cerevisiae possesses three related ammonium transporters, Mep1, Mep2 and Mep3, differing in their kinetic properties and in the level and regulation of their gene expression. The three Mep proteins belong to a family conserved in bacteria, plants and animals, which also includes proteins of the rhesus blood group family. In addition to its role in scavenging extracellular ammonium, the Mep2 protein has been proposed to act as an ammonium sensor, essential to pseudohyphal differentiation in response to ammonium limitation. To pursue the biochemical study of the Mep transporters, we raised polyclonal antibodies against the C-terminal tail of each Mep protein. When electrophoresed on SDS-polyacrylamide gel, the Mep1 and Mep3 proteins migrate as expected from their predicted size, whereas the Mep2 protein migrates as a high-molecular-weight smear. Protein deglycosylation with peptide-N-glycosidase F (PNGase F) indicates that, in contrast to Mep1 and Mep3, Mep2 is an asparagine-linked glycoprotein. Site-directed mutagenesis of the four potential N-glycosylation sites of Mep2 shows that Asn-4 of the protein's N-terminal tail is the only site that binds oligosaccharides. This provides evidence for the extracytosolic location of the Mep2 N-terminus. Consistently, treatment of intact protoplasts with proteinase K leads to specific proteolysis of the N-terminal tail of Mep2. The protein's C-terminus, on the other hand, is protected against protease degradation under these conditions, but digested after protoplast permeabilization, suggesting a cytoplasmic location for this part of the protein. Mep2 glycosylation is not required for pseudohyphal differentiation in response to ammonium starvation, and its absence causes only a slight reduction in the affinity of the transporter for its substrate.     

Inhibition of cell proliferation by D-ribose and deoxy-D-ribose

D-Ribose and deoxy-D-ribose inhibited DNA, RNA, and protein synthesis in a wide variety of cells (dividing and nondividing, normal and neoplastic, freely floating and substrate adhering, human and murine) at concentrations at which other monosaccharides have little or no effect. Inhibition was irreversible and proportional to the sugar concentration and time of contact. However, the first effects were seen only after 24 hr of incubation and progressed slowly to cell death. Whether the two sugars share the same mechanisms of action is not known. In any case, they deeply disturb metabolic processes in both dividing and nondividing cells.     

Altered expression of the two naturally occurring human insulin receptor variants in isolated adipocytes of non-insulin-dependent diabetes mellitus patients.

The human insulin receptor gene is expressed in two variant isoforms which differ by the absence (HIR-A) or presence (HIR-B) of 12 amino acids in the COOH-terminus of the extracellular alpha-subunit as a consequence of alternative splicing of exon 11. Expression of the two variant isoforms is regulated in a tissue-specific manner. In this study, we have measured the levels of the two receptor variants in isolated adipocytes from 10 non-insulin-dependent diabetes mellitus (NIDDM) and 11 normal subjects using an immunological assay, based on the ability of a human anti-receptor autoantibody to discriminate between HIR-A and HIR-B. Results indicate that levels of HIR-B variant are increased in NIDDM patients.