Factor-free and one-factor-promoted poly(U,C)-dependent synthesis of polypeptides in cell-free systems from Escherichia coli

α-Tropomyosin from rat cardiac muscle was shown by two-dimensional gel electrophoresis to become phosphorylated when tissue slices were incubated in Eagle's medium supplemented with ³²P_i. In the adult rat and mouse heart the level of phosphorylation was ～30%, but the level was much higher in the foetal heart (60–70%). A similar developmental trend was observed in skeletal muscle from the rat and mouse, where phosphorylated forms of both α- and β-tropomyosins were observed. When rat cardiac cells were grown in tissue culture in the presence of ³²P_i, radioactivity was incorporated into the region of the gel containing tropomyosin.     

Visualization of thrombin receptors on mouse embryo fibroblasts using fluorescein-amine conjugated human α-thrombin

The localization of thrombin receptors on mouse embryo (ME) cells has been examined by direct fluorescence microscopy using a fluorescein aminelabeled thrombin. Two fluorescein amines, 4-(N-6-aminoethyl thioureal)-fluorescein and 4-(N-6-aminohexyl thioureal)-fluorescein, were synthesized and attached to the carbohydrate moiety of highly purified human α-thrombin by periodate oxidation of the carbohydrate and selective reduction of the Schiff's base using sodium cyanoborohydride. Preparations of fluorescent thrombin with from 1 to 4 fluoresceins per molecule of thrombin retained their ability to proteolytically cleave fibrinogin to form fibrin clots, to bind to thrombin receptors on ME cells, and to initiate cell division. After incubating mitogenic concentrations of the fluorescein amine labeled thrombin with ME cells at 4°C, a diffuse fluorescent pattern was observed over the surface of the ME cells. This diffuse pattern was specific: it was not observed on cells from parallel cultures incubated with fluorescent thrombin plus a 20-fold excess of unlabeled thrombin. Thus, thrombin receptors appear to be distributed randomly over the surface of ME cells prior to interaction with thrombin. Increasing the temperature to 37°C following binding at 4° C resulted in a rapid dissociation of the fluorescent pattern from the cells leaving only the autofluorescent vesicles. This result may reflect the unique ability of thrombin to proteolytically cleave its own receptor.     

In vitro translation of maize ADH: Evidence for the anaerobic induction of mRNA

Total cellular RNA from anaerobically stressed maize seedling roots was used to stimulate in vitro translation of authentic maize alcohol dehydrogenase (ADH) in a rabbit reticulocyte lysate system. Total products from such reactions were displayed on NEPHGE-SDS two-dimensional gels and the Adhl-specific translation products were identified by using RNA from sib seedlings segregating for Adhl charge and size variants. The application of a rapid RNA isolation procedure allowed the efficient isolation of biologically active RNAs from small amounts of seedling material. Maize ADHs translated in vitro are identical in size to in vivo ADH. Further, no ADH was detected in the products of an in vitro translation reaction stimulated by total RNA from aerobically grown seedlings. This suggests that induction of ADH protein by anaerobic stress is accomplished by production of Adh mRNA rather than activation of sequestered mRNA. The mRNAs for maize ADH1 and ADH2 are among a small class of mRNAs induced during anaerobiosis.Research was supported by NSF Grant PCM 76-11009. M.D.B. is supported by National Institute of Health Grant PHS 5 T32 GM07227-04. R.J.F. is a Predoctoral Trainee in Genetics supported by National Institute of Health Training Grants 82 and 7757 from the National Institute of General Medical Sciences.     

Kinetics of microcolony formation of a soil oligotrophic bacterium, Agromonas sp.

Abstract The kinetics of budding/dividing of parent cells at different culture ages, spread on a fresh medium, was formulated by the following model N _t= N _∞ [1 − exp (− λ ( t − t _r)] where N _t is the number of budding/dividing cells in the parent population at time t , N _∞ is the expected number of budding/dividing cells at infinite time, λ is the rate of budding/dividing of parent cells, and t _r is the retardation time. The rate of budding/dividing λ decreased with the increase in the culture age of the parent cell population.     

Battling for Ribosomes: Translational Control at the Forefront of the Antiviral Response

In the early stages of infection, gaining control of the cellular protein synthesis machinery including its ribosomes is the ultimate combat objective for a virus. To successfully replicate, viruses unequivocally need to usurp and redeploy this machinery for translation of their own mRNA. In response, the host triggers global shutdown of translation while paradoxically allowing swift synthesis of antiviral proteins as a strategy to limit collateral damage. This fundamental conflict at the level of translational control defines the outcome of infection. As part of this special issue on molecular mechanisms of early virus–host cell interactions, we review the current state of knowledge regarding translational control during viral infection with specific emphasis on protein kinase RNA-activated and mammalian target of rapamycin-mediated mechanisms. We also describe recent technological advances that will allow unprecedented insight into how viruses and host cells battle for ribosomes.     

Visualization of RNA-protein interactions in living cells: FMRP and IMP1 interact on mRNAs

Protein expression depends significantly on the stability, translation efficiency and localization of mRNA. These qualities are largely dictated by the RNA-binding proteins associated with an mRNA. Here, we report a method to visualize and localize RNA-protein interactions in living mammalian cells. Using this method, we found that the fragile X mental retardation protein (FMRP) isoform 18 and the human zipcode-binding protein 1 ortholog IMP1, an RNA transport factor, were present on common mRNAs. These interactions occurred predominantly in the cytoplasm, in granular structures. In addition, FMRP and IMP1 interacted independently of RNA. Tethering of FMRP to an mRNA caused IMP1 to be recruited to the same mRNA and resulted in granule formation. The intimate association of FMRP and IMP1 suggests a link between mRNA transport and translational repression in mammalian cells.     

植物根毛生长发育及分子调控机理

植物根毛是植物吸收营养的主要器官, 了解根毛的发生、发育及遗传规律, 能对植物的养分吸收研究提供有利依据。文章旨在介绍植物根毛形态发生特性、发育生长过程及分子调控机理的研究进展, 利用比较基因组学方法研究农作物根毛形态和功能, 及有目的性的对根生长发育进行调控提供参考。研究发现植物根毛发育有反馈侧向抑制(lateral inhibition with feedback)和位置决定模式(position-dependent pattern of cell differentiation)两种方式。拟南芥根表皮细胞是以位置方式决定毛或非毛细胞发育类型, 已成为研究植物细胞命运和分化的模型。目前, 已经鉴定出控制根毛发育的基因, 包括一些转录因子如MYB家族蛋白TRIPTYCHON(TRY)、CAPRICE(CPC)和basic Helix-Loop-Helix (bHLH)蛋白GLABRA3、ENHANCER OF GLABRA3(EGL3)及WD-repeat蛋白等基因。最后针对根毛研究前景提出展望。