Identifying Darwinian Selection Acting on Different Human APOL1 Variants among Diverse African Populations

Disease susceptibility can arise as a consequence of adaptation to infectious disease. Recent findings have suggested that higher rates of chronic kidney disease (CKD) in individuals with recent African ancestry might be attributed to two risk alleles (G1 and G2) at the serum-resistance-associated (SRA)-interacting-domain-encoding region of APOL1. These two alleles appear to have arisen adaptively, possibly as a result of their protective effects against human African trypanosomiasis (HAT), or African sleeping sickness. In order to explore the distribution of potential functional variation at APOL1, we studied nucleotide variation in 187 individuals across ten geographically and genetically diverse African ethnic groups with exposure to two Trypanosoma brucei subspecies that cause HAT. We observed unusually high levels of nonsynonymous polymorphism in the regions encoding the functional domains that are required for lysing parasites. Whereas allele frequencies of G2 were similar across all populations (3%–8%), the G1 allele was only common in the Yoruba (39%). Additionally, we identified a haplotype (termed G3) that contains a nonsynonymous change at the membrane-addressing-domain-encoding region of APOL1 and is present in all populations except for the Yoruba. Analyses of long-range patterns of linkage disequilibrium indicate evidence of recent selection acting on the G3 haplotype in Fulani from Cameroon. Our results indicate that the G1 and G2 variants in APOL1 are geographically restricted and that there might be other functional variants that could play a role in HAT resistance and CKD risk in African populations.     

外源亚精胺对盐胁迫下白刺幼苗叶片抗氧化酶系统的影响

为进一步阐明盐生植物白刺耐盐性与多胺的关系,通过水培试验研究了叶面喷施亚精胺(Spd)对不同浓度NaCl胁迫下西伯利亚白刺幼苗叶片丙二醛(MDA)和超氧阴离子(O2)产生速率,以及抗氧化物酶系统和根系活力的影响.结果表明:叶面喷施0.1 mmol·L1 Spd 5 d后,可显著提高100和200 mmol·L1 NaCl胁迫下白刺幼苗叶片超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)的活性以及根系活力,降低了叶片MDA含量和O2的产生速率;而在0、50、300 mmol·L-1 NaC1处理下,外施Spd对白刺幼苗叶片上述指标无显著影响.研究结果证实,在100～200 mmol·L-1 NaCl胁迫范围内,外施亚精胺可能通过增强体内保护酶活性来显著降低活性氧水平,有效减轻盐胁迫对盐生植物白刺幼苗造成的过氧化伤害,从而增强白刺对盐环境的适应性.     

Saccharomyces cerevisiae proteins involved in hybrid DNA formation in vitro

RecA-like activities that can form hybrid DNA in vitro have been identified in a wide variety of organisms. We have previously described the strand exchange protein 1 (SEP1) from the yeast Saccharomyces cerevisiae that can form hybrid DNA in vitro. Purified as an Mr 132,000 polypeptide, recent molecular and immunological studies have now shown that the native form is an Mr 175,000 polypeptide containing strand exchange activity. The gene encoding SEP1 has been cloned and sequenced. The primary sequence failed to reveal any significant sequence homology to other sequences in data base searches. In vivo SEP1 was found to be essential for normal meiosis as cells containing a homozygous insertion mutation in the SEP1 gene failed to sporulate. In order to identify additional factors that are involved in hybrid DNA formation in S cerevisiae, we used an in vitro stimulation assay to identify proteins that reconstitute strand exchange activity in reactions containing limiting amounts of SEP1. We have identified two proteins that functionally interact with SEP1. First, an Mr 34,000 single-stranded DNA binding protein stimulated the reaction by lowering the requirement for SEP1 about 3-4 fold. This protein is a fragment of the large subunit of a hetero-trimeric complex called yRP-A (yRF-A) which is thought to be the functional eukaryotic equivalent of single-stranded DNA binding proteins in prokaryotes. The gene encoding this protein (RPA1) is essential for growth. Second, an Mr 33,000 polypeptide, termed Stimulatory Factor 1 (SF1), dramatically stimulated the SEP1 catalyzed reaction by lowering the requirement for SEP1 about 300 fold.(ABSTRACT TRUNCATED AT 250 WORDS)     

Basolateral K channels in an insect epithelium. Channel density, conductance, and block by barium

K channels in the basolateral membrane of insect hindgut were studied using current fluctuation analysis and microelectrodes. Locust recta were mounted in Ussing-type chambers containing Cl-free saline and cyclic AMP (cAMP). A transepithelial K current was induced by raising serosal [K] under short-circuit conditions. Adding Ba to the mucosal (luminal) side under these conditions had no effect; however, serosal Ba reversibly inhibited the short-circuit current (Isc), increased transepithelial resistance (Rt), and added a Lorentzian component to power density spectra of the Isc. A nonlinear relationship between corner frequency and serosal [Ba] was observed, which suggests that the rate constant for Ba association with basolateral channels increased as [Ba] was elevated. Microelectrode experiments revealed that the basolateral membrane hyperpolarized when Ba was added: this change in membrane potential could explain the nonlinearity of the 2 pi fc vs. [Ba] relationship if external Ba sensed about three-quarters of the basolateral membrane field. Conventional microelectrodes were used to determine the correspondence between transepithelially measured current noise and basolateral membrane conductance fluctuations, and ion-sensitive microelectrodes were used to measure intracellular K activity (acK). From the relationship between the net electrochemical potential for K across the basolateral membrane and the single channel current calculated from noise analysis, we estimate that the conductance of basolateral K channels is approximately 60 pS, and that there are approximately 180 million channels per square centimeter of tissue area.     

A new type of prosome-like particle, composed of small cytoplasmic RNA and multimers of a 21-kDa protein, inhibits protein synthesis in vitro

A large fraction of the translationally repressed non-globin messenger RNA in duck erythroblasts is present in non-polyribosomal free mRNP structures which sediment in the 30-40-S range ('35 S'). In 0.5 M KCl, they form core complexes which show a pronounced peak at about 32 S containing mRNA and a discrete spherical RNP particle with a diameter of about 12 nm and the typical morphology of a prosome [H.-P. Schmid et al. (1984) EMBO J. 3, 29-34]. Buoyant density measurements and chromatography on oligo(dT)-cellulose indicate that this particle is bound to mRNA; it can be released from the mRNA by treatment of the free mRNP fraction with SDS. This prosome-like particle inhibits the translation of mRNA in vitro. It is composed primarily of multimers of a single 21-kDa protein and at least one species of RNA of about 80-100 nucleotides. It is resistant to dissociation by 2 M CS2SO4 and 1% SDS; the 21-kDa protein is not attacked by proteinase K unless the particle is extracted with phenol prior to treatment with the protease. The small RNA moiety of the particle hybridizes to the poly(A)-rich mRNA derived from the free mRNPs, as well as to polyribosomal mRNA. These data indicate that prosomes may serve to regulate mRNA translation; they show furthermore that prosome-like particles (about 600 kDa mass) may be built of up to 25 molecules of a single specific protein, rather than of the entire set of about 20 prosomal proteins previously identified.     

Molecular and genetic analysis of the gene encoding the Saccharomyces cerevisiae strand exchange protein Sep1.

Vegetatively grown Saccharomyces cerevisiae cells contain an activity that promotes a number of homologous pairing reactions. A major portion of this activity is due to strand exchange protein 1 (Sep1), which was originally purified as a 132,000-Mr species (R. Kolodner, D. H. Evans, and P. T. Morrison, Proc. Natl. Acad. Sci. USA 84:5560-5564, 1987). The gene encoding Sep1 was cloned, and analysis of the cloned gene revealed a 4,587-bp open reading frame capable of encoding a 175,000-Mr protein. The protein encoded by this open reading frame was overproduced and purified and had a relative molecular weight of approximately 160,000. The 160,000-Mr protein was at least as active in promoting homologous pairing as the original 132,000-Mr species, which has been shown to be a fragment of the intact 160,000-Mr Sep1 protein. The SEP1 gene mapped to chromosome VII within 20 kbp of RAD54. Three Tn10LUK insertion mutations in the SEP1 gene were characterized. sep1 mutants grew more slowly than wild-type cells, showed a two- to fivefold decrease in the rate of spontaneous mitotic recombination between his4 heteroalleles, and were delayed in their ability to return to growth after UV or gamma irradiation. Sporulation of sep1/sep1 diploids was defective, as indicated by both a 10- to 40-fold reduction in spore formation and reduced spore viability of approximately 50%. The majority of sep1/sep1 diploid cells arrested in meiosis after commitment to recombination but prior to the meiosis I cell division. Return-to-growth experiments showed that sep1/sep1 his4X/his4B diploids exhibited a five- to sixfold greater meiotic induction of His+ recombinants than did isogenic SEP1/SEP1 strains. sep1/sep1 mutants also showed an increased frequency of exchange between HIS4, LEU2, and MAT and a lack of positive interference between these markers compared with wild-type controls. The interaction between sep1, rad50, and spo13 mutations suggested that SEP1 acts in meiosis in a pathway that is parallel to the RAD50 pathway.     

Electrical and adaptive properties of rod photoreceptors in bufo marinus. II. Effects of cyclic nucleotides and protaglandins

Substances known to alter cyclic nucleotide levels in cells were applied to the isolated toad retina and effects on rod electrical and adaptive behavior were studied. The retina was continually superfused in control ringer’s or ringer’s containing one or a combination of drugs, and rod activity was recorded intracellularly. Superfusion with cGMP, Bu(2)GMP, isobutylmethylxanthine (IBMX; a phosphodiesterase inhibitor), or PGF(2α) (a prostaglandin) caused effects in rods that closely match those observed when extracellular Ca(2+) levels were lowered. For example, short exposures (up to 6 min) of the retina to these substances caused depolarization of the membrane potential, increase in response amplitudes, and some changes in waveform; but under dark-adapted or partially light-adapted conditions receptor sensitivity was virtually unaffected. That is, the position of the V-log I curve on the intensity axis was determined by the prevailing light level, not by drug level. These drugs, like lowered extracellular Ca(2+), also decreased the period of receptor saturation after a bright-adapting flash, resulting in an acceleration of the onset of membrane and sensitivity recovery during dark adaptation.

Long-term (6-15 min) exposure of a dark-adapted retina to 5 mM IBMX or a combination of IBMX and cGMP caused a loss of response amplitude and a desensitization of the rods that was similar to that observed in rods after a long-term low Ca(2+) (10(-9)M) treatment. Application of high (3.2 mM) Ca(2+) to the retina blocked the effects of applied Bu(2)cGMP. PGE(1) superfusion mimicked the effects of increasing extracellular Ca(2+). The results show that increased cGMP and lowered Ca(2+) produce similar alterations in the electrical activity of rods. These findings suggest that Ca(2+) and cGMP are interrelated messengers. We speculate that low Ca(2+) may lead to increased intracellular cGMP, and/or that applied cGMP, and/or that applied cGMP may lower cytosol Ca(2+), perhaps by stimulating Ca(2+)- ATPase pumps in the outer segment.