A new Saccharomyces cerevisiae strain with a mutant Smt3-deconjugating Ulp1 protein is affected in DNA replication and requires Srs2 and homologous recombination for its viability

The Saccharomyces cerevisiae Srs2 protein is involved in DNA repair and recombination. In order to gain better insight into the roles of Srs2, we performed a screen to identify mutations that are synthetically lethal with an srs2 deletion. One of them is a mutated allele of the ULP1 gene that encodes a protease specifically cleaving Smt3-protein conjugates. This allele, ulp1-I615N, is responsible for an accumulation of Smt3-conjugated proteins. The mutant is unable to grow at 37 degrees C. At permissive temperatures, it still shows severe growth defects together with a strong hyperrecombination phenotype and is impaired in meiosis. Genetic interactions between ulp1 and mutations that affect different repair pathways indicated that the RAD51-dependent homologous recombination mechanism, but not excision resynthesis, translesion synthesis, or nonhomologous end-joining processes, is required for the viability of the mutant. Thus, both Srs2, believed to negatively control homologous recombination, and the process of recombination per se are essential for the viability of the ulp1 mutant. Upon replication, mutant cells accumulate single-stranded DNA interruptions. These structures are believed to generate different recombination intermediates. Some of them are fixed by recombination, and others require Srs2 to be reversed and fixed by an alternate pathway.     

Exploring structural features of the interaction between the scorpion toxinCnErg1 and ERG K+ channels

The gamma-KTx-type scorpion toxins specific for K+ channels were found to interact with ERG channels on the turret region, while alpha-KTx3.2 Agitoxin-2 binds to the pore region of the Shaker K+ channel, and alpha-KTx5.3 BmP05 binds to the intermediate region of the small-conductance calcium-activated K-channel (SK(Ca)). In order to explore the critical residues for gamma-KTx binding, we determined the NMR structure of native gamma-KTx1.1 (CnErg1), a 42 amino acid residues scorpion toxin isolated from the venom of the Mexican scorpion Centruro?des noxius Hoffmann, and we used computational evolutionary trace (ET) analysis to predict possible structural and functional features of interacting surfaces. The 1H-NMR three-dimensional solution structure of native ergtoxin (CnErg1) was solved using a total of 452 distance constraints, 13 3J(NH-Halpha) and 10 hydrogen bonds. The structure is characterized by 2 segments of alpha-helices and a triple-stranded antiparallel beta-sheet stabilized by 4 disulfide bridges. The ET and structural analysis provided indication of the presence of two important amino acid residue clusters, one hydrophobic and the other hydrophilic, that should be involved in the surface contact between the toxin and the channel. Some features of the proposed interacting surface are discussed.     

The complete genomic organization of the human MUC6 and MUC2 mucin genes

The complete genomic organization of the two mucin genes MUC2 and MUC6 was obtained by comparison of new and published mRNA sequences with newly available human genomic sequence. The two genes are located 38.5 kb apart in a head-to-head orientation within a gene complex on chromosome 11p15.5. The N-terminal organization of MUC6 is highly similar to that of MUC2, containing the D1, D2, D', and D3 Von Willebrand factor domains followed by the large tandem repeat domains located in exons 31 and 30, respectively. MUC6 has a much smaller C-terminal domain (101 amino acids) encoded by 2 exons containing only the CK domain, compared with MUC2, which has a C-terminal domain of 859 amino acids containing the D4, C, D, and CK domains, encoded by 19 exons. The gene structures agreed partially but not completely with predictions from gene prediction programs.     

Complex spatial distribution and dynamics of an abundant Escherichia coli outer membrane protein, LamB

Advanced techniques for observing protein localization in live bacteria show that the distributions are dynamic. For technical reasons, most such techniques have not been applied to outer membrane proteins in Gram-negative bacteria. We have developed two novel live-cell imaging techniques to observe the surface distribution of LamB, an abundant integral outer membrane protein in Escherichia coli responsible for maltose uptake and for attachment of bacteriophage lambda. Using fluorescently labelled bacteriophage lambda tails, we quantitatively described the spatial distribution and dynamic movement of LamB in the outer membrane. LamB accumulated in spiral patterns. The distribution depended on cell length and changed rapidly. The majority of the protein diffused along spirals extending across the cell body. Tracking single particles, we found that there are two populations of LamB--one shows very restricted diffusion and the other shows greater mobility. The presence of two populations recalls the partitioning of eukaryotic membrane proteins between 'mobile' and 'immobile' populations. In this study, we have demonstrated that LamB moves along the bacterial surface and that these movements are restricted by an underlying dynamic spiral pattern.     

Increased Na+ intake during gestation in rats is associated with enhanced vascular reactivity and alterations of K+ and Ca2+ function

Gestation is associated with decreased blood pressure and resistance to the effects of vasoconstrictor agents. A recent study showed that pregnant rats, on increased sodium intake, present physiological changes that resemble those observed in preeclampsia. We investigated the effects of sodium supplementation on reactivity and on potassium and Ca(2+) channel activity in blood vessels during gestation. Sodium supplements, 0.9% or 1.8% NaCl as drinking water, were given to nonpregnant and pregnant rats for 7 days (last week of gestation). Reactivity to phenylephrine (PE), KCl, arginine vasopressin (AVP), and tetraethylammonium (TEA) was measured in aortic rings under modulation of potassium and calcium channels. TEA, a nonselective K(+) channel inhibitor, induced concentration-dependent responses in aortic rings from nonpregnant but not in those from pregnant rats. The response to TEA was restored in rings from pregnant rats after preincubation with 10 mmol/l KCl. Sodium supplementation did not affect the response to TEA in the aortas of pregnant animals. After sodium supplementation, maximum responses to PE and AVP were decreased and increased in aortic rings from nonpregnant and pregnant rats, respectively. Cromakalim (an ATP-sensitive K(+) channel activator)-induced inhibition of the responses to the three vasoconstrictors was more striking in aorta from nonpregnant than pregnant rats on regular diet, whereas it produced similar inhibition in tissues from both groups of animals on 0.9% and 1.8% NaCl. NS-1619 (a Ca(2+)-sensitive K(+) activator) elicited heightened effects in the aortas of pregnant animals receiving 0.9% NaCl supplementation. Nifedipine (a Ca(2+) channel blocker) caused greater inhibition of the contractile responses in tissues from nonpregnant rats on regular diet, and its action was increased in pregnant rats on sodium-supplemented diets. These data demonstrate that augmented sodium intake during gestation in the rat is linked with the reversal of gestational-associated resistance to vasopressors and indicate that this is an experimental model showing some features of gestational hypertension.     

Nanoscale organization of multiple GPI-anchored proteins in living cell membranes

Cholesterol and sphingolipid-enriched "rafts" have long been proposed as platforms for the sorting of specific membrane components including glycosyl-phosphatidylinositol-anchored proteins (GPI-APs), however, their existence and physical properties have been controversial. Here, we investigate the size of lipid-dependent organization of GPI-APs in live cells, using homo and hetero-FRET-based experiments, combined with theoretical modeling. These studies reveal an unexpected organization wherein cell surface GPI-APs are present as monomers and a smaller fraction (20%-40%) as nanoscale (<5 nm) cholesterol-sensitive clusters. These clusters are composed of at most four molecules and accommodate diverse GPI-AP species; crosslinking GPI-APs segregates them from preexisting GPI-AP clusters and prevents endocytosis of the crosslinked species via a GPI-AP-selective pinocytic pathway. In conjunction with an analysis of the statistical distribution of the clusters, these observations suggest a mechanism for functional lipid-dependent clustering of GPI-APs.     

Origin of bovine follicular fluid and its effect during in vitro maturation on the developmental competence of bovine oocytes

Protein supplementation during in vitro maturation can profoundly affect both the rate and overall efficiency of the maturation procedure. The present study was conducted to assess the ability of different concentrations (1, 5, and 10%) of bovine follicular fluid (bFF) to support in vitro maturation of oocytes and subsequent developmental capacity. The bFF was derived either from competent follicles ( > 8 mm) obtained by transvaginal recovery following superovulation or from a pool of small follicles (2-5 mm) from abbatoir-derived ovaries. Bovine oocytes were cultured for 24 h in synthetic oviduct fluid medium (m-SOF) supplemented with polyvinylpyrrolidone. Following fertilization and embryo culture, more oocytes (P < 0.05) reached the blastocyst stage when oocytes were cultured with 5% bFF from competent follicles (41 +/- 3.7%) compared with bFF derived from small follicles (16 +/- 2.9%). Estradiol and recombinant human follicle stimulating hormone added to the competent bFF during maturation acted in synergy to increase blastocyst production rate (P < 0.05); this blastocyst production rate (57 +/- 1.2%) was higher than those obtained with the addition of these two hormones to bFF derived from small follicles (26 +/- 2.9%). The quality of blastocysts obtained was reflected by inner cell mass (51.30 +/- 3.5 and 25.50 +/- 3.7) and trophectoderm cell numbers (99.72 +/- 2.5 and 94.80 +/- 4.7) for bFF from competent and small follicles, respectively. In conclusion, follicular fluid originating from competent follicles increased the developmental competence of abbatoir-derived oocytes.     

Influence of the ionic strength on the heat-induced aggregation of the globular protein beta-lactoglobulin at pH 7

The influence of the ionic strength on the structure of beta-lactoglobulin aggregates formed after heating at pH 7 has been studied using static and dynamic light scattering. The native protein depletion has been monitored using size exclusion chromatography. Above a critical association concentration (CAC) well-defined clusters are formed containing about 100 monomers. The CAC increases with decreasing ionic strength. The so-called primary aggregates associate to form self similar semi-flexible aggregates with a large scale structure that is only weakly dependent on the ionic strength. The local density of the aggregates increases with increasing ionic strength. At a critical gel concentration, Cg, the size of the aggregates diverges. Cg decreases from 100 g/l without added salt to 1 g/l at 0.4M NaCl. For C > Cg the system gels except at high ionic strength close to Cg where the gels collapse under gravity and a precipitate is formed.