带有特定染色体片段的mini-F质粒所发动的染色体复制对于recA基因的依赖性

构建了一些带有大肠杆菌的特定染色体片段的mini-F质粒,使它们通过同源重组整合在dnaA46细菌的染色体的预定位置上,然后测定整合抑制菌株(sin)在40℃中染色体复制对recA基因的依赖性。实验结果说明,Sin菌株对recA基因的依赖性决定在质粒的整合位置。整合在oriC近旁的Sin菌株不依赖于recA基因;整合在oriC和terC中间的只在丰富培养基上是依赖的;整合在rerC附近的在不丰富的培养基上也依赖于recA基因。     

带有IS1的mini—F质粒所发动的染色体复制对于recA基因的依赖性

我们曾报道整合的F′质粒所发动的大肠杆菌染色体复制依赖于recA基因,而整合的F质粒则不。构建带有IS1的mini-F质粒,它们的复制起点分别来自F或F′质粒。这些质粒的整合抑制菌株中都有约20％是recA依赖的,不管这一mini-F质粒的复制起点来自F或F′质粒,也不管这一质粒在游离状态中的复制方向是单向或双向。实验结果说明,质粒的整合位置是决定由整合质粒所发动的染色体复制对recA基因的依赖性的主要因素。     

质粒的复制特性和整合后在发动大肠杆菌染色体复制中对recA基因的依赖性的研究

大肠杆菌的温度敏感的DNA复制发动突变型dnaA46在42℃中不能生长而形成菌落,质粒或噬菌体的整合使它能生长。前文[2]报道了F质粒整合后所发动的染色体复制依赖于recA基因。本文报道5种质粒和2种噬菌体整合后所发动的染色体复制对recA基因的依赖性的研究结果。实验结果说明,依赖与否和它们在游离状态中复制方向无关,从而否定了recA基因的作用是把质粒或噬菌体的游离状态的单向复制发动机构改变为整合状态的双向复制发动饥构这一假设。     

大肠杆菌K-12dnaA突变型的R6K整合抑制菌株的多起点染色体复制

大肠杆菌K-12的温度敏感复制发动缺陷突变(dnaA46)菌株LC381不能在42℃中进行染色体复制。在42℃中选取R6K质粒整合抑制菌株,用标记频率测定法测得这一菌株在30℃中染色体复制从正常的复制起点起始,在42℃中则从另外三个起点起始,其中两个曾见报道,把重组突变recA56引入这一菌株,发现由接近正常复制起点起始的染色体复制不受recA突变的影响,由接近正常复制终点起始的染色体复制则受到阻碍,说明由这一位置起始的染色体复制依赖于recA基因。这一实验结果和我们的其他报道相符。     

大肠杆菌中整合状态的F′质粒复制起点的克隆和分析

用标记获救法克隆了整合状态的F′质粒的复制起点,证明了由这一复制起点构成的mini-F质粒在不亲和性和对吖啶橙的敏感性方面和自主状态的F′质粒都没有不同。对这一复制起点和来自自主状态的F质粒的复制起点进行了亚克隆,并作限制性内切酶酶切分析比较,没有发现两者在结构上有差异。本文的结果提示,F质粒和F′质粒在发动染色体复制中对recA基因的依赖性的不同,可能与质粒整合在染色体上的位置不同有关。     

recA基因通过同源重组途径参与由整合质粒发动的大肠杆菌染色体复制

我们在前文中报道由整合的F'质粒所发动的大肠杆菌染色体的复制依赖于recA基因。本文报道有关recA、recB、recC以及lexA等在染色体复制中的作用,实验结果说明,recA基因通过同源重组途径而不是通过SOS途径参与复制,而且recA基因和Chi热点无关。实验结果还说明,RecBC酶的依赖于ATP的双链DNA外切核酸酶活性和recA基因的作用无关。     

质粒R144drd3对于大肠杆菌DNA复制发动突变型dnaP18的非整合抑制

通过接合转移,把F1、F11、P、W、X、Ⅰ型的14种质粒分别引入大肠杆菌复制发动突变型dnaP 18,发现只有Ⅰ型质粒R144对于dnaP18具有抑制作用,消阻遏质粒R144 drd3的抑制能力高于质粒R144约一万倍而达到完全的抑制。以下事实说明R144 drd3并不通过整合到dnaP18细菌的染色体上而带来对于dnaP18的抑制:(1)dnaP18(R144drd3)细菌的染色体标记的转移频率在10~(-7)以下,而其质粒标记Km~R的转移频率约10~(-1);(2)这些菌株的DNA抽提物的电泳图谱和电子显微镜照相都说明质粒DNA的存在。 用带有质粒R144 drd3的E.coli作为供体,用E.coli dnaP18菌株作为受体,通过噬菌体P1转导得到的两种Km~R转导子中一种能在42℃形成菌落,而另一种则不能;将转座子Tn10转座到R144drd3上以后,同样使受体成为能在42℃形成菌落或不能形成菌落两类。这些结果表明,质粒R144drd3上存在着与dnaP18抑制有关的特定区域或基因。     

异形胞分化蓝细菌dnaA温度敏感型突变体的构建

以能分化异形胞的蓝细菌(Anabaenasp.PCC7120)为材料,采用重组PCR在体外对控制DNA复制起始的dnaA基因进行定点突变后克隆到整合质粒中,再通过三亲本杂交将整合质粒转移到Anabaena PCC7120中,以分离和筛选温度敏感型突变体。结果成功获得Anabaena PCC 7120 dnaA高温敏感性突变体。研究表明,利用重组PCR技术可在体外实现对Anabaena PCC 7120的dnaA的定点突变,并可通过同源重组双交换成功实行整合质粒中突变基因对野生型基因的置换,使突变基因插入到细胞染色体中,进而成功构建温度敏感型突变菌株。     

线形质粒

质粒是染色体外的遗传因子,是一种双链环状的DNA分子,质粒本身含有复制的遗传结构,能在细胞质中独立自主地进行自我复制。它是一个复制子。一些质粒也能整合到细菌染色体中随染色体的复制而复制。质粒一般都带有某些抗性基因。     

质粒RP4的一株杀宿主温度敏感突变体的研究

质粒是细菌染色体外的遗传因子。一般来说质粒的存在与否并不影响宿主细胞的正常生长。但是当宿主细胞存在某些缺陷时,质粒所带的某些基因可以代替宿主缺陷基因的功能,这一点很早就为F′的遗传学分析所说明。与此相反,已有一些报道表明,某些基因发生了突变的质粒,或者通过重组DNA技术所形成的某些杂种质粒(例如带生长激素释放抑制因子基因的杂种质粒PSOM 11-3),可以严重影响宿主细胞的生长,甚至杀死宿主细胞。因此质粒基因与宿主基因的相互关系的研究,不仅有助于进一步弄清原核生物基因的调控机制,也可以借此深入了解某些突变质粒或杂种质粒对宿主产生有害影响的原因。这在遗传工程上也是有一定价值的。     

Characteristics of the membranes of the pellicle of the ciliatePseudomicrothorax dubius

Summary The membranes of the pellicle of the ciliatePseudomicrothorax dubius are investigated using thin section electron microscopy and freeze-fracture replicas. The plasma membrane is covered by a surface coat and is connected to the outer alveolar membrane by short, sometimes branched, bridges. The inner alveolar membrane is coated on both sides. The epiplasm lies in intimate contact with the cytoplasmic surface of this membrane, and there is a corresponding deposit on the other surface. This deposit is regularly striated.The epiplasmic layer and the alveoli are interrupted at sites of cytotic activity,e.g., the attachment sites of trichocysts, the cytoproct, and the parasomal sacs. The striated deposit ends where the epiplasm ends, indicating a direct relationship between these two epimembranous layers.There is a deposit along the sides of the first part of the tip of the trichocysts, and in this region the trichocyst membrane is free of intramembranous particles.The membrane of the parasomal sacs has a coat on both surfaces. That on the extraplasmic surface is similar to the surface coat of the plasma membrane. The origin of the cytoplasmic coat is unknown. The cytotic activity of these sacs is indicated by their highly irregular profiles.     

The early development of the tail and the transformation of the shape of the nucleus of the spermatid of the domestic fowl,Gallus gallus

Summary The differentiation of the spermatid, especially in reference to the formation of the flagellum, and transformation of the shape of the nucleus was investigated in the domestic fowl.In the early stage of the spermatid, a prominent Golgi apparatus appears around the centrioles. The Golgi vesicles then surround the axial-filament complex which develops from the distal centriole. These vesicles fuse to form continuous membrane at the earliest stage of flagellar formation, and in the succeeding stage Golgi lamellae are attached to the plasma membrane of the developing flagellum. From these observations, it is assumed that Golgi apparatus may be a source of the membrane system of the flagellum.The microtubules distributed around the nucleus form the circular manchette. The anterior region of the nucleus with the manchette is cylindrical in shape and the posterior region without it remains irregular in shape. When the circular manchette has been completed, the whole nucleus acquires a slender cylindrical shape. The circular manchette then changes into the longitudinal manchette. The nuclei of spermatids without a longitudinal manchette are abnormal in shape. In view of these observations it is assumed that the nuclear shaping of the spermatid may be accomplished by circular manchette and the maintenance of shape of the elongated nucleus by longitudinal manchette.The authors wish to thank Mr. Takayuki Mori for his helpful suggestions and technical advices     

Characterization of the composition of the aqueous humor and the vitreous body of the eye of the frog Rana temporaria L

This study aimed to analyze the aqueous humor (AH) and the vitreous body (VB) of the eye of the adult frog Rana temporaria L. as a representative species of amphibians, which lead a semi-terrestrial life. The presence of collagen, albumin, uric acid and electron donors was shown in both media; however, there are slight differences in their concentrations. To determine collagen, a spectral-fluorescent probe, cyanine dye, was used. The presence of collagen in AH of the frog was found at the first time. The total content of electron donors (ascorbic and uric acids, tryptophan, and tyrosine) in VB and HA was roughly estimated at ~ 1.5 × 10^− 4 mol/L. Both VB and AH absorb light in similar UV regions. The total protein and albumin contents in AH were found to be somewhat higher than those in VB. The uric acid content was at an equally low level in both intraocular media. It is supposed that the similarity of VB and AH compositions shown in this work is due to some exchange between VB and AH contents in the course of accommodation. The role of intraocular fluids in physiological functions of the eye and in protecting the retina against UV light is discussed.     

Observations on the permeability of the choriocapillaris of the eye

Summary The choriocapillaris is a fenestrated capillary bed located posterior to the retinal pigment epithelium. It serves as the main source of supply to the photoreceptors, retinal pigment epithelium, and other cells of the outer retina. The permeability of these capillaries to intravenously injected ferritin (MW — approx. 480,000; mol. diam. 11 nm) was examined in the mouse, rabbit, and guinea pig, each of which is characterized by a different type of retinal vascularization. In all three species, the bulk of the ferritin remained in the capillary lumina, where it appeared to be blocked at the level of the diaphragmed fenestrae. Some ferritin was present in endothelial cell vacuoles. The results confirm previous work on the rat choriocapillaris and indicate that the barrier function of the choriocapillary endothelium is present even among species in which the retinal circulation differs significantly.Supported by NIH grant EY03418