Existence of high abundance antiproliferative mRNA's in senescent human diploid fibroblasts

Polyadenylated RNA isolated from senescent human diploid fibroblasts (HDF) inhibited DNA synthesis in proliferation-competent cells after microinjection, whereas polyadenylated RNA from young HDF had no inhibitory effect. Polyadenylated RNA from young cells made quiescent by removal of serum growth factors had a slight inhibitory effect on DNA synthesis. The abundance level of inhibitor messenger RNA (mRNA) from senescent cells was estimated at 0.8 and that of quiescent cells at 0.005 percent. These results demonstrate the existence of one or more antiproliferative mRNA's in nonproliferating normal human cells; these RNA's code for factors that either work antagonistically to initiators of DNA synthesis or regulate the expression of the initiators in some way. The abundance level of the inhibitory mRNA in senescent cells indicates the feasibility of developing a complementary DNA probe that will be useful in studying cell cycle control mechanisms.     

Rapid switching of plant gene expression induced by fungal elicitor

The pattern of messenger RNA synthesis in suspension-cultured bean cells (Phaseolus vulgaris L.) was analyzed by blot hybridization and in vitro translation of newly synthesized messenger RNA. The RNA was separated from preexisting RNA by organomercurial affinity chromatography after in vivo labeling with 4-thiouridine. The elicitor induced the synthesis of messenger RNA's encoding phenylalanine ammonia-lyase, chalcone synthase, and chalcone isomerase, three enzymes of phenylpropanoid metabolism involved in the synthesis of isoflavonoidderived phytoalexins. This is part of a rapid and extensive change in the pattern of messenger RNA synthesis directing production of a set of proteins associated with expression of disease resistance.     

Comparison of messenger RNA in photoperiodically induced and noninduced Xanthium buds

In response to the floral stimulus, Xanthium buds synthesize relatively more messenger RNA than do vegetative buds. This is demonstrated by fractionation, on methylated albumin-kieselguhr columns, of a mixture of nucleic acids from vegetative and induced buds, one being labeled with uridine-H(3) and the other with uridine-2-C(14). While floral induction stimulates a small increase in messenger RNA synthesis as revealed by labeling intact plants, this difference can be magnified by labeling excised buds in solution. From experiments with excised buds from Xanthium plants, it is concluded that buds from photoperiodically induced plants contain more messenger RNA than buds from noninduced ones do.     

Protein synthesis: its control in erythropoiesis

Erythropoiesis in the fetal mouse provides a model to study several important aspects of the regulation of cell differentiation and differentiated protein synthesis. Changes in the patterns of hemoglobins formed during fetal and postfetal development are shown to be associated with the substitution of the liver erythroid cell line. In the course of differentiation of yolk sac erythroid cells there are at least two classes of proteins distinguishable with respect to dependence on continued RNA formatoin. The bulk of nuclear proteins, "nondifferentiated" proteins, appear to be dependent on relatively short-lived messenger RNA while synthesis of differentiated proteins, the hemoglobins, proceeds on relatively stable molecules of messenger RNA. Hemoglobin formation occurs in those cells which are actively synthesizing DNA and dividing. On the average, two to three cell divisions may occur after the formation and stabilization of the messenger RNA for globin. Yolk sac erythropoiesis, at least from day 10 of gestation, is unresponsive to erythropoietin. By comparison, in fetal liver erythropoiesis, the hormone, erythropoietin, acts selectively on the most immature erythroid cell precursor to induce differentiation, cell replication, and hemoglobin formation. The erythropoietin responsive cell in the liver is apparently differentiated from the progenitor, pluripotential stem cell and committed to erythroblast formation and hemoglobin synthesis on exposure to the hormone. The initial effects of erythropoietin on macromolecular synthesis are to stimulate RNA synthesis, which temporally is followed by cell replication and the increase in hemoglobin formation. During liver erythropoiesis, there appears to be a transition from hemoglobin synthesis dependent on RNA formation to hemoglobin synthesis directed by relatively stable messenger RNA.     

Photoreceptor regulation of CONSTANS protein in photoperiodic flowering

Many plants flower in response to seasonal fluctuations in day length. The CONSTANS (CO) gene of Arabidopsis promotes flowering in long days. Flowering is induced when CO messenger RNA expression coincides with the exposure of plants to light. However, how this promotes CO activity is unknown. We show that light stabilizes nuclear CO protein in the evening, whereas in the morning or in darkness the protein is degraded by the proteasome. Photoreceptors regulate CO stability and act antagonistically to generate daily rhythms in CO abundance. This layer of regulation refines the circadian rhythm in CO messenger RNA and is central to the mechanism by which day length controls flowering.     

泛素/26S蛋白酶体途径在水稻中的生物学功能研究进展

生物体内的蛋白质降解方式有两种,一种不需要能量,一种需要能量。而泛素/26S蛋白酶体途径便是目前已知的依赖ATP、高效、有高度选择性的蛋白降解途径。它介导了真核生物中80%~85%的蛋白质降解,几乎参与到植物生长发育的各个环节,是植物体内蛋白高效专一降解最重要、最精细的调控机制之一。概述了泛素蛋白酶体途径,重点阐述了泛素结合酶E2和泛素连接酶E3的蛋白结构及其在水稻生长发育、激素信号传导、生物和非生物胁迫响应中的生物学功能及机制,并对进一步研究进行了展望,将有助于揭示泛素/26S蛋白酶体途径在水稻生长发育中的精细调控过程,并为水稻抗逆育种提供了指导和借鉴。