Semidominant effect of the l(1)ts403 (sbr10) mutation on nondisjunction of sex chromosomes in meiosis in Drosophila melanogaster females exposed to heat

The sbr gene of Drosophila melanogaster belongs to the NXF (nuclear export factor) family responsible for the mRNA transport from nucleus to cytoplasm. We have shown that in the heat-exposed (37 degrees C, 1 h) females, the l(1)ts403 (sbr10) mutation leads, in particular, to the high-frequency nondisjunction and loss of sex chromosomes in meiosis. For this trait, the incomplete dominance of the sbr10 mutation is observed. At the same time, the sbr10 mutation is recessive for many other traits of the heat-exposed flies: reduced viability, low fertility, impaired synthesis of the heat shock proteins, etc. The females heterozygous for the null allele (Df(1)vL4, a deletion eliminating gene srb) do not differ from females homozygous for the wild-type allele in frequency of the heat shock-induced nondisjunction and loss of sex chromosomes in meiosis. Because of this, the sbr10 mutation can be assigned to the gain-of-function alleles (those gaining the dominance function). Expression of the mutant sbr10 allele against the background of the wild-type allele suggests that in the heat shock-exposed females, the heat-modified product of this ts allele has a strong effect on sex chromosome disjunction in meiosis.     

Mutation-selection networks of cancer initiation: tumor suppressor genes and chromosomal instability

In this paper, we derive analytic solutions of stochastic mutation-selection networks that describe early events of cancer formation. A main assumption is that cancer is initiated in tissue compartments, where only a relatively small number of cells are at risk of mutating into cells that escape from homeostatic regulation. In this case, the evolutionary dynamics can be approximated by a low-dimensional stochastic process with a linear Kolmogorov forward equation that can be solved analytically. Most of the time, the cell population is homogeneous with respect to relevant mutations. Occasionally, such homogeneous states are connected by 'stochastic tunnels'. We give a precise analysis of the existence of tunnels and calculate the rate of tunneling. Finally, we calculate the conditions for chromosomal instability (CIN) to precede inactivation of the first tumor suppressor gene. In this case, CIN is an early event and a driving force of cancer progression. The techniques developed in this paper can be used to study arbitrarily complex mutation-selection networks of the somatic evolution of cancer.     

Molecular evolution of rDNA external transcribed spacer and phylogeny of sect. Petota (genus Solanum)

The 5(') external transcribed spacer (ETS) region of ribosomal DNA of 30 species of Solanum sect. Petota and the European Solanum dulcamara were compared. Two structural elements can be distinguished in the ETS: (i). a variable region (VR), demonstrating significant structural rearrangements and (ii). a conservative region (CR), evolving mainly by base substitutions. In VR, a conservative element (CE) with similarity to the ETS of distantly related Nicotiana is present. The ancestral organization of ETS (variant A) was found for non-tuber-bearing species of ser. Etuberosa, tuber-bearing wild potatoes of Central American ser. Bulbocastana, Pinnatisecta, and Polyadenia and S. dulcamara. Duplication of CE took place in the ETS of species from ser. Commersoniana and Circaeifolia (variant B). South American diploids and Mexican polyploids from superser. Rotata also possess two CE, and additionally two duplications around CE1 are present in VR (variant C). Three major lineages could be distinguished: non-tuber-bearing species of ser. Etuberosa, tuber-bearing Central American diploids and all South American species radiated from a common ancestor at early stages of evolution, indicating a South American origin of the tuber-bearing species. Later, Central and South American diploids evolved further as independent lineages. South American species form a monophyletic group composed of series with both stellata and rotata flower morphology. Solanum commersonii represents a sister taxon for all rotata species, whereas ser. Circaeifolia diverged earlier. Two main groups, C1 and C2, may be distinguished for species possessing ETS variant C. C1 contains ser. Megistacroloba, Conicibaccata, Maglia, and Acaulia, whereas all diploids of ser. Tuberosa are combined into C2. A closer relationship of Solanum chacoense (ser. Yungasensa) to the C2 group was found. The origin of polyploid species Solanum maglia, Solanum acaule, Solanum tuberosum, Solanum iopetalum, and Solanum demissum is discussed.     

Contextual Features of Higher Plant mRNA 5"-Untranslated Regions

Computer analysis of nucleotide sequences of 5"-untranslated regions (5"-UTR) of higher plant mRNA adopted from the EMBL nucleotide sequence database was carried out. It was demonstrated that the average nucleotide frequencies of the leader sequences and adjacent regions of basal promoters are similar, whereas introns and 3"-UTR have a higher content of T and a lower content of C. A particular 5"-UTR contextual feature is a misbalance in the content of complementary nucleotides, probably caused by negative influence of the stable secondary structure on the translation properties of the leader sequence. Approximately 20% of 5"-UTR possess AUG triplets, i.e., twice as much as it has been estimated earlier. The properties of the open reading frames of the leader sequence (uORF) and presumable causes of their high content in 5"-UTR of eukaryotic mRNAs are discussed. The nature of correlation between some features of uORFs and protein-coding gene sequences is analyzed. It is demonstrated that in effectively translated mRNAs the leader AUG triplets are more frequently located in a nonoptimal context, whereas the terminating codons of uORFs more frequently exist in the optimal one. A hypothesis is put forward that the efficiency of termination at the uORF stop codon might substantially interfere with the mRNA translation activity.     

Dark recovery of diploid yeast cells after simultaneous exposure to UV-irradiation and hyperthermia

Quantitative regularities of dark recovery of wild-type diploid yeast cells of Saccharomyces cerevisiae simultaneously treated with UV-light (254 nm) and high temperatures (53-56 degrees C) were studied. Under this combined action, the constant of recovery, which defines the probability of elimination of the UV-radiation induced damage per unit of time, did not depend on the temperature of irradiation. It was shown that both the irreversible component of cell damage and the number of cells that died without division gradually increased as the temperature of exposure increased. It is concluded, on this basis, that the mechanism of synergistic interaction of UV-radiation and hyperthermia is related not to the inhibition of dark recovery itself, but to the increase in the shape of irreversibly damaged cells incapable of recovering from the induced damage.     

Protein S1 counteracts the inhibitory effect of the extended Shine-Dalgarno sequence on translation

There are two major components of Escherichia coli ribosomes directly involved in selection and binding of mRNA during initiation of protein synthesis-the highly conserved 3' end of 16S rRNA (aSD) complementary to the Shine-Dalgarno (SD) domain of mRNA, and the ribosomal protein S1. A contribution of the SD-aSD and S1-mRNA interactions to translation yield in vivo has been evaluated in a genetic system developed to compare efficiencies of various ribosome-binding sites (RBS) in driving beta-galactosidase synthesis from the single-copy (chromosomal) lacZ gene. The in vivo experiments have been supplemented by in vitro toeprinting and gel-mobility shift assays. A shortening of a potential SD-aSD duplex from 10 to 8 and to 6 bp increased the beta-galactosidase yield (four- and sixfold, respectively) suggesting that an extended SD-aSD duplex adversely affects translation, most likely due to its redundant stability causing ribosome stalling at the initiation step. Translation yields were significantly increased upon insertion of the A/U-rich S1 binding targets upstream of the SD region, but the longest SD remained relatively less efficient. In contrast to complete 30S ribosomes, the S1-depleted 30S particles have been able to form an extended SD-aSD duplex, but not the true ternary initiation complex. Taken together, the in vivo and in vitro data allow us to conclude that S1 plays two roles in translation initiation: It forms an essential part of the mRNA-binding track even when mRNA bears a long SD sequence, and through the binding to the 5' untranslated region, it can ensure a substantial enhancing effect on translation.     

Effect of aeration conditions on the biosynthesis of carminomycin by an actinomadura carminata culture]

The effect of the aeration rate on biosynthesis of carminomycin by Actinomadura carminata and biochemical changes in the fermentation broth on the use of 3 complex media of different composition was studied. The carminomycin-producing organism can grow and produce the antibiotic within the ranges of the aeration changes from 0.98 to 18.56 mgO2/1-min. A decrease in the maximum rate of oxygen dissolution up to 0.98 mgO2/1-min resulted in some decrease in the activity level. Intensive aeration, i.e. 18.56 mgO2/1-min induced suppression of the antibiotic production by 25 per cent.     

Molecular dynamics imaging in micropatterned living cells

Micropatterning approaches using self-assembled monolayers of alkyl thiols on gold are not optimal for important imaging modalities in cell biology because of absorption of light and scattering of electrons by the gold layer. We report here an anisotropic solid microetching (ASOMIC) procedure that overcomes these limitations. The method allows molecular dynamics imaging by wide-field and total internal reflection fluorescence (TIRF) microscopy of living mammalian cells and correlative platinum replica electron microscopy.     

Conformational changes in CLIP-170 regulate its binding to microtubules and dynactin localization

Cytoplasmic linker protein (CLIP)-170, CLIP-115, and the dynactin subunit p150(Glued) are structurally related proteins, which associate specifically with the ends of growing microtubules (MTs). Here, we show that down-regulation of CLIP-170 by RNA interference results in a strongly reduced accumulation of dynactin at the MT tips. The NH(2) terminus of p150(Glued) binds directly to the COOH terminus of CLIP-170 through its second metal-binding motif. p150(Glued) and LIS1, a dynein-associating protein, compete for the interaction with the CLIP-170 COOH terminus, suggesting that LIS1 can act to release dynactin from the MT tips. We also show that the NH(2)-terminal part of CLIP-170 itself associates with the CLIP-170 COOH terminus through its first metal-binding motif. By using scanning force microscopy and fluorescence resonance energy transfer-based experiments we provide evidence for an intramolecular interaction between the NH(2) and COOH termini of CLIP-170. This interaction interferes with the binding of the CLIP-170 to MTs. We propose that conformational changes in CLIP-170 are important for binding to dynactin, LIS1, and the MT tips.     

Ultrastructure of Chenopodium rubrum L. apices during the effect of fusicoccin and photoperiodic induction

Plant transition from vegetative to reproductive development is associated with ultrastructural changes in stem apices. Those seen in Chenopodium rubrum L. under the influence of fusicoccin in many ways resemble those induced by a short-day treatment favourable to flowering. This suggests that fusicoccin can play a definite (physiological) role in plant development.