The alpha- and beta-tubulin folding pathways

The alpha-beta tubulin heterodimer is the subunit from which microtubules are assembled. The pathway leading to correctly folded alpha- and beta-tubulins is unusually complex: it involves cycles of ATP-dependent interaction of newly synthesized tubulin subunits with cytosolic chaperonin, resulting in the production of quasi-native folding intermediates, which must then be acted upon by additional protein cofactors. These cofactors form a supercomplex containing both alpha- and beta-tubulin polypeptides, from which native heterodimer is released in a GTP-dependent reaction. Here, we discuss the current state of our understanding of the function of cytosolic chaperonin and cofactors in tubulin folding.     

甘蔗细平象的研究

甘蔗细平象Trockorhopalus humeralis Chevrolat是云南甘蔗上的一种毁灭性地下害虫,以幼虫和成虫在地下蔗头内为害,为害期8-10个月。据1989年调查,受害蔗每亩损失500-3000kg,严重的无收。此虫1年发生1代,以成虫在蔗头内越冬,有喜湿性,不能飞翔,主要通过沟河流水传播。在河川坝地,沙壤土中虫口较多;宿根年限越长的甘蔗受害越重。建议蔗稻轮作;缩短甘蔗宿根年限;早春翻挖有虫蔗蔸烧毁;结合新植蔗下种,宿根蔗松蔸培土施用甲基异柳磷或铁灭克等颗粒杀虫剂进行防治。     

濒危植物——长喙毛茛泽泻的雌雄配子体发育

长喙毛茛泽泻 Ranalisma rostratum stapf 小孢子母细胞的减数分裂过程为连续型,四分体为左右对称型。成熟花粉为三胞花粉。花药绒毡层为变形绒毡层。雌蕊由多数单室子房构成,每子房中含一具双珠被、薄珠心的倒生胚珠。胚囊发育为葱型。成熟胚囊中三个反足细胞退化;二个极核分别位于中央细胞的两端,其体积相差明显。这种极核分布可能与反足细胞过早退化有关。     

Cellulolytic enzymes of fungi isolated from wood materials

Species of Cunninghamella, Gliocladium deliquescens, Trichoderma harzianum and T. koningii were isolated from rotten wood chips. When grown on medium containing cellulose, all except Cunninghamella produced the three primary enzymes (exoglucanase, endoglucanase and -glucosidase) of the cellulase complex. The patterns for enzyme production, changes in mycelial mass and pH of the induction medium for T. harzianum and T. koningii were closely similar, and were distinguishable from those of G. deliquescens.     

Expression of Ty-lacZ fusions in Saccharomyces cerevisiae

We have determined the nucleotide sequence of about 520 bp spanning the 5' delta regions (Figure 1) of two Tyl elements. There is an open reading frame running out of the deltas for at least 180 nucleotides into the internal region of each element. The functional significance of these open reading frames has been tested by fusing them to a defective E.coli lacZ gene. Expression of B-galactosidase in yeast transformants containing these fusions shows that Tyl elements contain functional translation signals.     

Esterase and malate dehydrogenase isozyme polymorphisms in 15 Artemia populations.

1. Starch gel electrophoresis of adult brine shrimps from 15 populations revealed little intrapopulation polymorphism in NAD-dependent malate dehydrogenase (MDH) isozymes or in the two fastest esterases (demonstrated with alpha-naphthyl propionate as substrate). 2. Interpopulation differences could be summarized as three different electrophoresis band patterns for the five- to seven-banded MDH isozymes and another three patterns for the two fastest esterases. 3. These differences in electrophoresis patterns divide the 15 Artemia populations into four categories (each containing one to seven populations) which may be distinguished by isozyme content and which are congruent with categories established by the criterion of reproductive isolation in an earlier study.     

Metabolism of [14C]diethylstilboestrol epoxide by rat liver in vitro.

1. The trans-epoxide of diethylstilboestrol and its pinacolone were synthesized chemically and the pinacolone shown to be formed from the epoxide by a non-enzymic process. 2. [14C]Diethylstiboestrol epoxide was converted by rat liver microsomal fraction into 4'-hydroxypropiophenone by a new type of cleavage reaction involving mono-oxygenase. Conditions for the formation of this metabolite and also water-soluble products were investigated together with the effect of inhibitors. A sex-difference in the conversion of diethylstilboestrol epoxide into 4'-hydroxypropiophenone and to polar and water-soluble products was observed. 3. Diethylstilboestrol epoxide was found to be a relatively stable compound that did not form a glutathione conjugate readily without further microsomal activation. A purified preparation of epoxide hydratase did not enhance its rate of conversion into the pinacolone. 4. Diethylstilboestrol epoxide was found to have about one-tenth the oestrogenic activity of diethylstilboestrol as measured by the increase in uterine weight or the induction of peroxidase in immature rat uteri. It was inactive as a mutagen when tested for its ability to inhibit bacteriophage phi X174 DNA viral replication. 5. The possible role of diethylstilboestrol epoxide as an intermediate in the metabolism of diethylstilboestrol and in mediating the harmful effects of this synthetic estrogen is discussed.     

DNA fragments associated with chromosome scaffolds

Following extensive digestion of HeLa metaphase chromosomes with either Hae III endonuclease or micrococcal nuclease, nonhistone protein scaffolds may be isolated. Scaffolds isolated after Hae III digestion have about 1.5% of the chromosomal DNA attached to them. This DNA is heterogeneous in size, ranging from about 0.2 to 20 kbp. It can be cleaved with either Eco RI or Hae III - Eco RI, producing a series of repeated fragments, of which the most abundant is 1.7 kbp in length. The 1.7-kdp fragment is tandemly repeated and is enriched (about 50-fold) in the scaffold-associated DNA. It is located primarily on human chromosome 1 and is probably a component of human satellites II and III. Scaffolds isolated after micrococcal nuclease digestion have about 0.1% of chromosomal DNA attached. This DNA is present in two size classes - fragments larger than 10 kbp and fragments approximately 0.2 kbp long. Restriction enzyme digestion of this DNA gives no prominent repeated fragments. Its reassociation kinetics are similar to those of total DNA, indicating that it is not enriched in either highly repetitive or middle repetitive sequences.