Meiosis-dependent tyrosine phosphorylation of a yeast protein related to the mouse p51ferT

The FER locus of the mouse encodes two mRNA species: one is constitutively transcribed, giving rise to a 94 kDa tyrosine kinase (p94^ferT); the second is a meiosis-specific RNA that gives rise to a 51 kDa tyrosine kinase (p51^ferT). The p51^ferT RNA and protein accumulate in primary spermatocytes that are in prophase of the first meiotic division. By using polyclonal antibodies directed against synthetic peptides derived from the unique amino-terminus of the mouse p51^ferT, a 51 kDa phosphotyrosyl protein — p51^y — was identified in Saccharomyces cerevisiae. The p51^y protein is constitutively expressed in yeast, but in meiotic cells, concomitantly with commitment to meiotic recombination, its level of phosphorylation on tyrosine residues is increased. A different pattern of phosphorylation is observed on serine residues: at early meiotic times the level is decreased, while in later meiotic time the level increases, reaching the vegetative level. When p51^ferT is ectopically expressed in yeast, it is active, leading to preferential phosphorylation of an approx. 65 kDa protein. A similar pattern of phosphorylation by p51^ferT is seen in mammalian cells.     

Degradation and transformation of humic substances by saprotrophic fungi: processes and mechanisms

Humic substances represent the main carbon reservoir in the biosphere, estimated at 1600 × 10¹⁵ g C. Due to their crucial role in reductive and oxidative reactions, sorption, complexation and transport of pollutants, minerals and trace elements, sustaining plant growth, soil structure and formation, and control of the biogeochemistry of organic carbon in the global ecosystem, humic substances are extremely important to environmental processes. Saprotrophic fungi active in the decomposition process of humic substances include mainly ascomycetes and basidiomycetes, which are both common in the upper layers of soils. White rot and litter decomposing fungi are the most important organisms in the degradation and mineralization of refractory organic matter (OM), whereas ascomycetes are mainly involved in the modification and polymerization of humic substances. The mechanisms of degradation probably involve mainly a variety of non specific oxidizing enzymes. This review provides an overview of the subject, while bridging two main disciplines: soil OM chemistry and fungal microbiology. It is aimed to highlight problems, unsolved questions and hypotheses.     

Diurnal oscillation of SBE expression in sorghum endosperm

Spatial and temporal expression patterns of the sorghum SBEI, SBEIIA and SBEIIB genes, encoding, respectively, starch branching enzyme (SBE) I, IIA and IIB, in the developing endosperm of sorghum (Sorghum bicolor) were studied. Full-length genomic and cDNA clones for sorghum were cloned, and the SBEIIA cDNA was used together with gene-specific probes for sorghum SBEIIB and SBEI. In contrast to sorghum SBEIIB, which was expressed primarily in endosperm and embryo, SBEIIA was also expressed in vegetative tissues. All three genes shared a similar temporal expression profile during endosperm development, with a maximum activity at 15-24 d after pollination. This differed from barley and maize, in which SBEI gene activity showed a significantly later onset compared to that of SBEIIA and SBEIIB. Expression of the three SBE genes in the sorghum endosperm exhibited a diurnal rhythm during a 24-h cycle.     

Autosegregation of enzyme loci in agamospermous progenies of triploid plants of sugar beet (<Emphasis Type=Italic>Beta vulgaris</Emphasis> L.)

The ratios of the phenotypic classes of glucosephosphate isomerase (GPI2) and malate dehydrogenase (MDH1 and MDH2) were studied in agamospermous progenies of triploid sugar beet plants. The ratio of the phenotypic classes of these enzymes corresponds to the calculations based on the assumption of polyteny of chromosomes carrying alleles of the enzyme loci accompanied by the loss of extra copies of the alleles in the first division of a cell entering embryogenesis. An increase in the gene dosage due to polyteny leads to the appearance in the progeny with a definite frequency of alleles that were absent in the original parental plant. The notions of “meiotic autosegregation” and “mitotic autosegregation” characteristic of meiotic and mitotic agamospermy are introduced, as well as the term locus polygenotype characterizing not only the allelic composition and the number of chromosomes, but also the number of chromatids carrying alleles of the marker locus in the cell before its entry into embryogenesis.     

Aym1, a mouse meiotic gene identified by virtue of its ability to activate early meiotic genes in the yeast Saccharomyces cerevisiae

Our understanding of the molecular mechanisms that operate during differentiation of mitotically dividing spermatogonia cells into spermatocytes lags way behind what is known about other differentiating systems. Given the evolutionary conservation of the meiotic process, we screened for mouse proteins that could specifically activate early meiotic promoters in Saccharomyces cerevisiae yeast cells, when fused to the Gal4 activation domain (Gal4AD). Our screen yielded the Aym1 gene that encodes a short peptide of 45 amino acids. We show that a Gal4AD-AYM1 fusion protein activates expression of reporter genes through the promoters of the early meiosis-specific genes IME2 and HOP1, and that this activation is dependent on the DNA-binding protein Ume6. Aym1 is transcribed predominantly in mouse primary spermatocytes and in gonads of female embryos undergoing the corresponding meiotic divisions. Aym1 immunolocalized to nuclei of primary spermatocytes and oocytes and to specific type A spermatogonia cells, suggesting it might play a role in the processes leading to meiotic competence. The potential functional relationship between AYM1 and yeast proteins that regulate expression of early meiotic genes is discussed.     

Iron uptake mechanism in the chrysophyte microalga Dinobryon

The mechanism of iron uptake in the chrysophyte microalga Dinobryon was studied. Previous studies have shown that iron is the dominant limiting elements for growth of Dinobryon in the Eshkol reservoir in northern Israel, which control its burst of bloom. It is demonstrated that Dinobryon has a light-stimulated ferrireductase activity, which is sensitive to the photosynthetic electron transport inhibitor DCMU and to the uncoupler CCCP. Iron uptake is also light-dependent, is inhibited by DCMU and by CCCP and also by the ferrous iron chelator BPDS. These results suggest that ferric iron reduction by ferrireductase is involved in iron uptake in Dinobryon and that photosynthesis provides the major reducing power to energize iron acquisition. Iron deprivation does not enhance but rather inhibits iron uptake contrary to observations in other algae.     

Diversity of β-Globin Mutations in Israeli Ethnic Groups Reflects Recent Historic Events

We characterized nearly 500 β-thalassemia genes from the Israeli population representing a variety of ethnic subgroups. We found 28 different mutations in the β-globin gene, including three mutations (β^S, β^C, and β^O-Arab) causing hemoglobinopathies. Marked genetic heterogeneity was observed in both the Arab (20 mutations) and Jewish (17 mutations) populations. On the other hand, two ethnic isolates—Druze and Samaritans—had a single mutation each. Fifteen of the β-thalassemia alleles are Mediterranean in type, 5 originated in Kurdistan, 2 are of Indian origin, and 2 sporadic alleles came from Europe. Only one mutant allele—nonsense codon 37—appears to be indigenous to Israel. While human habitation in Israel dates back to early prehistory, the present-day spectrum of β-globin mutations can be largely explained by migration events that occurred in the past millennium.