Vernalization-mediated epigenetic silencing by a long intronic noncoding RNA

Vernalization is an environmentally-induced epigenetic switch in which winter cold triggers epigenetic silencing of floral repressors and thus provides competence to flower in spring. In Arabidopsis, winter cold triggers enrichment of tri-methylated histone H3 Lys(27) at chromatin of the floral repressor, FLOWERING LOCUS C (FLC), and results in epigenetically stable repression of FLC. This epigenetic change is mediated by an evolutionarily conserved repressive complex, polycomb repressive complex 2 (PRC2). Here, we show that a long intronic noncoding RNA [termed COLD ASSISTED INTRONIC NONCODING RNA (COLDAIR)] is required for the vernalization-mediated epigenetic repression of FLC. COLDAIR physically associates with a component of PRC2 and targets PRC2 to FLC. Our results show that COLDAIR is required for establishing stable repressive chromatin at FLC through its interaction with PRC2.     

Synthesis of nonribosomal RNA by lymphocytes: a response to phytohemagglutinin treatment

When lymphocytes are stimulated to enlarge and divide by treatment with phytohemagglutinin, most of the rapidly synthesized RNA is nonribosomal. The phenomenon is a response by lymphocytes to stimulation by phytohemagglutinin, rather than a general concomitant of lymphocyte growth.     

Polycomb proteins targeted by a short repeat RNA to the mouse X chromosome

To equalize X-chromosome dosages between the sexes, the female mammal inactivates one of her two X chromosomes. X-chromosome inactivation (XCI) is initiated by expression of Xist, a 17-kb noncoding RNA (ncRNA) that accumulates on the X in cis. Because interacting factors have not been isolated, the mechanism by which Xist induces silencing remains unknown. We discovered a 1.6-kilobase ncRNA (RepA) within Xist and identified the Polycomb complex, PRC2, as its direct target. PRC2 is initially recruited to the X by RepA RNA, with Ezh2 serving as the RNA binding subunit. The antisense Tsix RNA inhibits this interaction. RepA depletion abolishes full-length Xist induction and trimethylation on lysine 27 of histone H3 of the X. Likewise, PRC2 deficiency compromises Xist up-regulation. Therefore, RepA, together with PRC2, is required for the initiation and spread of XCI. We conclude that a ncRNA cofactor recruits Polycomb complexes to their target locus.     

The Xist RNA gene evolved in eutherians by pseudogenization of a protein-coding gene

The Xist noncoding RNA is the key initiator of the process of X chromosome inactivation in eutherian mammals, but its precise function and origin remain unknown. Although Xist is well conserved among eutherians, until now, no homolog has been identified in other mammals. We show here that Xist evolved, at least partly, from a protein-coding gene and that the loss of protein-coding function of the proto-Xist coincides with the four flanking protein genes becoming pseudogenes. This event occurred after the divergence between eutherians and marsupials, which suggests that mechanisms of dosage compensation have evolved independently in both lineages.     

多缸发动机气门间隙两次调整法原理分析

多缸发动机气门间隙的调整方法有逐缸调整法和两次调整法。两次调整法由于步骤简便而得到广泛应用。但在实际工作中 ,由于操作者对其调整原理不清 ,造成调整失误。为了更好的指导实践 ,本文将根据多缸发动机工作循环和配气相位来分析两次调整法的调整原理。1　调整原理配气相位是以曲轴的转角来表示进、排气门实际开启和关闭的时刻及进、排气门开启的延续时间 ,用环形图表示配气相位图 ,如图 1所示。通常 ,为了使进气量增多 ,废气排除干净 ,进、排气门都需提前开启和延迟关闭 ,即气门延续开启对应的曲轴转角均大于 1 80 。进气门早开和排气…     

Binding of ARF and beta-COP to Golgi membranes: possible regulation by a trimeric G protein

The binding of cytosolic coat proteins to organelles may regulate membrane structure and traffic. Evidence is presented that a small guanosine triphosphate (GTP)-binding protein, the adenosine diphosphate ribosylation factor (ARF), reversibly associates with the Golgi apparatus in an energy, GTP, and fungal metabolite brefeldin A (BFA)-sensitive manner similar to, but distinguishable from, the 110-kilodalton cytosolic coat protein beta-COP. Addition of beta gamma subunits of G proteins inhibited the association of both ARF and beta-COP with Golgi membranes that occurred upon incubation with guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S). Thus, heterotrimeric G proteins may function to regulate the assembly of coat proteins onto the Golgi membrane.     

L9(34)正交试验设计对白花蛇舌草愈伤组织诱导方案的优化

[目的]探究不同外植体、激素配比及光质对白花蛇舌草愈伤组织诱导的影响。[方法]采用正交试验法,以白花蛇舌草不同部位为外植体,进行较适外植体取材部位、光质和愈伤组织诱导激素配比的筛选。[结果]以新抽发的幼嫩茎尖为外植体对愈伤组织的诱导效果较好,以MS＋2,4-D3.5mg/L＋KT0.5mg/L培养基在白光条件下培养较为有利于白花蛇舌草诱导愈伤组织。[结论]试验进一步优化了白花蛇舌草愈伤组织的诱导方案,为开发利用地方植物资源奠定了基础。     

一种球状病毒对近海几种贝类的感染

报道了一种球状病毒对近海几种贝类的自然感染情况。并分别采用投喂、浸泡划伤等方法人工感染绣凹螺、滨螺和幼鲍,该病毒直径约９０～１４０ｎｍ。存在于血细胞或结缔组织细胞中,在近海几种贝类体内有广泛分布,但其致病性不同,同时还研究了病毒对温度的敏感性,结果表明２０℃以上病毒的繁殖力降低。     

HPLC法快速检测李子酒中多种有机酸

通过7种有机酸标准样品的高效液相色谱(HPLC)分析建立了果汁和果酒中7种重要有机酸的定性、定量比对与计算标准。该方法快速、简便,在李子酒有机酸的检测中应用结果良好;定性定量了酒中含有的3种重要的有机酸即草酸、酒石酸和L-苹果酸。