Short-fibre formation during cellulose degradation by cellulolytic fungi

Summary All cell-free filtrates of 26 fungal strains containning cellulase activities degraded native cellulose to both reducing sugar and insoluble short fibres. Low-molecular components from the crude filtrates could also degrade native cellulose into short fibres, not accompanied with the production of reducing sugar. Short fibre formation played an important role in cellulose degradation to make the substrate more accessible to attack of cellulases.     

Photoinactivation of photosystem II by cumulative exposure to short light pulses during the induction period of photosynthesis

Photoinactivation of Photosystem (PS) II in vivo was investigated by cumulative exposure of pea, rice and spinach leaves to light pulses of variable duration from 2 to 100 s, separated by dark intervals of 30 min. During each light pulse, photosynthetic induction occurred to an extent depending on the time of illumination, but steady-state photosynthesis had not been achieved. During photosynthetic induction, it is clearly demonstrated that reciprocity of irradiance and duration of illumination did not hold: hence the same cumulative photon exposure (mol m^–2) does not necessarily give the same extent of photoinactivation of PS II. This contrasts with the situation of steady-state photosynthesis where the photoinactivation of PS II exhibited reciprocity of irradiance and duration of illumination (Park et al. (1995) Planta 196: 401–411). We suggest that, for reciprocity to hold between irradiance and duration of illumination, there must be a balance between photochemical (qP) and non-photochemical (NPQ) quenching at all irradiances. The index of susceptibility to light stress, which represents an intrinsic ability of PS II to balance photochemical and non-photochemical quenching, is defined by the quotient (1-qP)/NPQ. Although constant in steady-state photosynthesis under a wide range of irradiance (Park et al. (1995). Plant Cell Physiol 36: 1163–1169), this index of susceptibility for spinach leaves declined extremely rapidly during photosynthetic induction at a given irradiance, and, at a given cumulative photon exposure, was dependent on irradiance. During photosynthetic induction, only limited photoprotective strategies are developed: while the transthylakoid pH gradient conferred some degree of photoprotection, neither D1 protein turnover nor the xanthophyll cycle was operative. Thus, PS II is more easily photoinactivated during photosynthetic induction, a phenomenon that may have relevance for understorey leaves experiencing infrequent, short sunflecks.Abbreviations D1 protein psbA gene product - DTT dithiothreitol - F_v, F_m, F_o variable, maximum, and initial (corresponding to open traps) chlorophyll fluorescence yield, respectively - NPQ non-photochemical quenching - PS Photosystem - Q_A primary quinone acceptor of PS II - qP photochemical quenching coefficient     

蓝氏贾第虫核被膜缺口的电镜观寨

双滴虫类是迄今所知的现存最原始的真核生物类群。以蓝氏贾第虫作为双滴虫类的代表,对其细胞核进行了电镜观察。除了未见有核仁外,还发现其核被膜的横切面上存在有缺口。在缺口的边缘处,核内膜与校外膜是相互连接着的,表明并非切片时所造成的假象。核被膜缺口处常有一核纤层样的薄层分隔核质与细胞质。用高锰酸钾固定细胞以求只保存膜结构时,核被膜缺口仍然可见,上述的薄层即未见到。核被膜缺口的发现证实了李靖炎（１９７９）的核被膜起源假说所作出的推断。     

Hox homeodomain proteins exhibit selective complex stabilities with Pbx and DNA.

Eight of the nine homeobox genes of the Hoxb locus encode proteins which contain a conserved hexapeptide motif upstream from the homeodomain. All eight proteins (Hoxb-1-Hoxb-8) bind to a target oligonucleotide in the presence of Pbx1a under conditions where minimal or no binding is detected for the Hox or Pbx1a proteins alone. The stabilities of the Hox-Pbx1a-DNA complexes vary >100-fold, with the proteins from the middle of the locus (Hoxb-5 and Hoxb-6) forming very stable complexes, while Hoxb-4, Hoxb-7 and Hoxb-8 form complexes of intermediate stability and proteins at the 3'-side of the locus (Hoxb-1-Hoxb-3) form complexes which are very unstable. Although Hox-b proteins containing longer linker sequences between the hexapeptide and homeodomains formed unstable complexes, shortening the linker did not confer complex stability. Homeodomain swapping experiments revealed that this motif does not independently determine complex stability. Naturally occurring variations within the hexapeptides of specific Hox proteins also do not explain complex stability differences. However, two core amino acids (tryptophan and methionine) which are absolutely conserved within the hexapeptide domains appear to be required for complex formation. Removal of N- and C-terminal flanking regions did not influence complex stability and the members of paralog group 4 (Hoxa-4, b-4, c-4 and d-4), which share highly conserved hexapeptides, linkers and homeodomains but different flanking regions, form complexes of similar stability. These data suggest that the structural features of Hox proteins which determine Hox-Pbx1a-DNA complex stability reside within the precise structural relationships between the homeodomain, hexapeptide and linker regions.     

生物复苏——大绝灭后生物演化历史的第一幕

生命史是一部生物界短期,快速剧变与长期,慢速稳定相互交替的历史。大绝灭（即集群绝灭）事件反映了全球环境的大突变,点断了地质历史中的生命记录及其发展历程,预示着生物界的演化出现了最有意义的飞跃,近年来尝试研究大绝灭后全球生物界的残存－复苏及其基本型式,并探索复苏的控制因素,标志着地质科学中一个重心的转移（即从大绝灭转向其后的生物残存与复苏的研究）。生物复苏揭示了大绝灭后生物演化历史的第一幕,其研究的     

Kinetics of retroviral production from the amphotropic ΨCRIP murine producer cell line

Rapidly expanding development and practice of gene therapy requires the availability of large quantities of high titer retroviral supernatants. One way to achieve high retroviral titers is through improved understanding of the kinetics of retroviral production and decay, and the subsequent development of improved cell culture methods. In the present study we investigated the effects of different operational modes on the retroviral production of the NIH 3T3 fibroblast derived amphotropic murine retroviral producing cell line pMFG/CRIP. Semi-continuous culture (exchange of 50% of medium volume daily) was found to promote cell growth and enhance retroviral production. The rapid medium exchange resulted in significantly larger amounts of high titer supernatants and an extended production phase as compared to the batch control cultures. The specific viral productivity of the pMFG/CRIP cells was in the range of 10 to 40 infectious viruses produced per thousand producer cells per day. The CV-1 African Green Monkey kidney cell line was used as the infection target. Lowering the serum level form 20% to 10% improved retroviral production slightly. However, at lower serum levels (1%, 5% and 10% (v/v)) growth of the producer cell line, and thus retroviral production, was directly proportional to the serum level. The half-life of the virus at 37°C was found to be 5.5 hours. Promoting the growth of producer cell lines can improve retroviral vectors titers and viral production. High cell density systems that allow for rapid cell growth and waste product removal are likely to be used to generate high-titer retroviral supernatants.     

大鼠卵巢促黄体激素/人绒毛膜促性腺激素受体cDNA的克隆和在昆虫细胞中的高效表达

促黄体激素/人绒毛膜促性腺激素受体(LH/hCG receptor)是一种与G-蛋白偶联的糖蛋白。本文报道了从大鼠卵巢cDNA库中筛选LH/hCG受体cDNA及其在昆虫细胞中的高效表达。LH/hCG受体cDNA全长2403bp,编码受体信号肽和成熟受体674个氨基酸。用多角体病毒表达载体pVL1393,LH/hCG受体cDNA在昆虫细胞中得到高效表达。在非还原和还原条件下的SDS-PAGE分析显示,用亲和层析分离纯化的受体表观分子量分别为120Kd和92Kd。经配基结合和Scatchard Plot分析表明,其与hCG反应的Kd为8.4×10~(-9)mol/L,与CHO细胞表达产物相似。     

肿瘤抑制基因APCmRNA在豚鼠脑中的分布

APC基因是1991年被发现的一类肿瘤抑制基因,它被定位于人第5号染色体5q21处。APC基因如发生缺失或突变,则易患直肠肿瘤,并伴有部分先天痴呆的病例。本工作在孟帆已获得的APC基因在豚鼠中的同源cDNA的基础上,完成了对它的亚克隆,并利用原位杂交和RNA酶保护分析的方法,对它在脑中的分布进行了研究。发现APCmRNA主要在海马、大脑和小脑中表达;嗅球中杂交信号稍弱,脑干中最弱。海马中阳性细胞主要是锥体细胞,小脑中则主要是内层颗粒细胞。在一个月大的豚鼠胚胎的脑中也观察到相似的表达型式。进一步的研究有助于我们更好地了解神经发育和先天痴呆发生的分子机制。     

一个恢复力受单基因控制的水稻CMS育性回复突变体

利用￣（６０）Ｃｏ－γ射线对具有印尼水田谷细胞质的籼稻细胞质雄性不育系Ⅱ－３２Ａ干种子进行诱变处理,获得了一育性回复突变体Ｔ２４。育性基因未纯合的突变体分离出可育株和完全不育株,比例为３∶１;其与Ⅱ－３２Ａ和珍汕９７Ａ测交,Ｆ１代分离出１∶１的可育株和不育株。育性稳定株系与Ⅱ－３２Ａ和珍汕９７Ａ杂交,Ｆ２分离成３∶１的可育株和不育株。表明其育性回复是由一对基因显性突变所致。这一突变体对不育系的育性恢复机制不同于明恢６３、２０９６４等恢复系,后者表现为两对显性恢复基因作用。未观察到Ｔ２４与亲本Ⅱ－３２Ａ除育性以外的其他性状的差异,因而两者构成育性恢复基因的近等基因系。本文还对不育系育性回复类型和Ｔ２４的理论意义与育种价值进行了讨论。     

中药凌霄花的药理学考察

实验结果表明,凌霄花对离体猪冠状动脉条具有抑制收缩的作用;对大鼠血栓形成有抑制作用;能加快红细胞电泳,增加红细胞电泳率,使血液红细胞处于分散状态;对离体孕子宫能显著增强收缩活性,增加收缩频率及增强收缩强度。以上结果可初步说明,凌霄花行血去瘀的作用及其“孕妇慎用”的合理性。凌霄花的３种混淆品（白泡桐花,毛泡桐花,兰考泡桐花）的药理作用与凌霄花不同,故不能作凌霄花使用。