Greater Length of Ribonucleic Acid Synthesized by Chromatin-bound Polymerase from Auxin-treated Soybean Hypocotyls

An investigation has been made of the RNA synthesized by chromatin-bound RNA polymerase from soybean hypocotyls (Glycine max var. Wayne). Polymerase activity is 4- to 5-fold higher with chromatin from tissue treated with 2,4-dichlorophenoxyacetic acid, a synthetic auxin, compared to untreated tissue. Thin layer chromatography of the RNA hydrolysis products and acrylamide gel electrophoresis of the RNA synthesized by the chromatin show that increased activity induced by 2,4-dichlorophenoxyacetic acid is due primarily to the production of longer RNA chains, with only 20 to 50% increase in the number of RNA chains. The observation that 2,4-dichlorophenoxyacetic acid treatment leads to greater rates of RNA synthesis, producing longer chains in unit time, suggests that one manifestation of auxin activity is in activation of RNA polymerase I (ribosomal RNA polymerase).     

Two functions encoded by adenovirus early region 1A are responsible for the activation and repression of the DNA-binding protein gene.

Human adenovirus early region 1A (E1A) gene products differentially regulate the expression of early region 2A (E2A) encoding the DNA-binding protein (DBP). In a microinjection system, plasmids containing the DBP gene associated with both its early (map coordinate 75) and late (coordinate 72) promoters, or only with the early promoter, are inefficiently expressed, and the presence of E1A DNA is required for full expression. In contrast, the E2A plasmid in which the DBP gene is associated solely with its late promoter, efficiently produces DBP, the synthesis of which is significantly inhibited by an E1A gene product. To identify which of the E1A products is responsible for either activation or repression of DBP gene expression, two E1A mutants (Ad5hr1 and Ad2/5pm975) have been tested in the microinjection system in the presence of different DBP plasmids containing either one or both promoters. The results obtained indicate that the product encoded by the E1A 13S mRNA is responsible for the stimulation of DBP produced from the early promoter and that the 12S mRNA codes for the product which represses the synthesis of DBP from the late promoter. These results were confirmed using clones in which the E2A early or late promoter was associated to the chloramphenicol acetyltransferase (CAT) gene and assayed for CAT activity after cell transfection in the absence or in the presence of wild-type or mutant E1A plasmids, and we have also shown that this promoter-dependent regulation is reflected in the relative amount of specific DBP mRNA.     

Characterization of a class of small auxin-inducible soybean polyadenylated RNAs

Four new auxin-responsive RNAs from soybean (Glycine max (L.) Merr., var. Wayne) are described. The RNAs were identified by hybridization to three cDNA probes obtained from a library enriched for sequences which increase in abundance within 60 min after 2,4-D (2,4-dichlorophenoxyacetic acid) treatment. These RNAs appear to define a new class of small (i.e. approximately 550 nucleotides) RNAs that respond extremely rapidly to application of exogenous auxin. In excised elongating hypocotyl sections, an increase in the abundance of these RNAs can be detected 2 to 5 min after treatment with 50 M 2,4-D. This response is half maximal after 10 min and reaches steady state in 60 min. RNA blot analysis shows that these RNAs are expressed differentially in various parts of the seedling. The degree of inducibility by auxin is also organ-specific, with the elongating hypocotyl being the most responsive of the organs tested. The RNAs display identical response specificities with one exception. Accumulation of one RNA, designated 10A, is completely abolished by simultaneous addition of cycloheximide and 2,4-D. This RNA also displays a different 2,4-D dose response than other RNAs examined. These results suggest that more than one mechanism is involved in rapid modulation of gene expression by auxin.     

An Auxin-Responsive Promoter Is Differentially Induced by Auxin Gradients during Tropisms

We constructed a chimeric gene consisting of a soybean small auxin up RNA (SAUR) promoter and leader sequence fused to an Escherichia coli [beta]-glucuronidase (GUS) open reading frame and a 3[prime] untranslated nopaline synthase sequence from Agrobacterium tumefaciens. This chimeric gene was used to transform tobacco by Agrobacterium-mediated transformation. In R2 etiolated transgenic tobacco seedlings, GUS expression occurred primarily in elongation regions of hypocotyls and roots. In green plants, GUS was expressed primarily in the epidermis and cortex of stems and petioles, as well as in elongation regions of anther filaments in developing flowers. GUS expression was responsive to exogenous auxin in the range of 10-8 to 10-3 M. During gravitropism and phototropism, the GUS activity became greater on the more rapidly elongating side of tobacco stems. Auxin transport inhibitors and other manipulations that blocked gravitropism also blocked the asymmetric distribution of GUS activity in gravistimulated stems. Light treatment of dark-grown seedlings resulted in a rapid decrease in GUS activity. Light-induced decay in GUS activity was fully reversed by application of auxin. Taken together, our results add support for the formation of an asymmetric distribution of auxin at sites of action during tropism.     

Selective Modulation of RNA Polymerase I Activity during Growth Transitions in the Soybean Seedling

RNA polymerase I and II activities were measured in tissues of the soybean (Glycina max, var. Wayne) hypocotyl where dramatic changes in the relative level of RNA synthesis are associated with normal and auxin-induced growth transitions. When assayed in isolated nuclei, the activity of RNA polymerase I changed much more than the activity of RNA polymerase II during these growth transitions. The activity of RNA polymerase I expressed in the nuclei generally showed a positive correlation with the relative level of RNA synthesis (i.e. accumulation) of that tissue. Following solubilization of the RNA polymerases from these isolated nuclei and fractionation of them on DEAE-cellulose, the activity of RNA polymerase I relative to that of RNA polymerase II showed smaller changes during these growth transitions than when assayed in the nuclei. Thus, these data indicate that the activity of RNA polymerase I is significantly modulated in the nucleus, up or down depending upon the growth state, during growth transitions in the soybean in addition to lesser changes which occur in the apparent level of the enzyme.     

An auxin-dependent distal organizer of pattern and polarity in the Arabidopsis root

Root formation in plants involves the continuous interpretation of positional cues. Physiological studies have linked root formation to auxins. An auxin response element displays a maximum in the Arabidopsis root and we investigate its developmental significance. Auxin response mutants reduce the maximum or its perception, and interfere with distal root patterning. Polar auxin transport mutants affect its localization and distal pattern. Polar auxin transport inhibitors cause dramatic relocalization of the maximum, and associated changes in pattern and polarity. Auxin application and laser ablations correlate root pattern with a maximum adjacent to the vascular bundle. Our data indicate that an auxin maximum at a vascular boundary establishes a distal organizer in the root.     

Integrity of White Matter is Compromised in Mice with Hyaluronan Deficiency

Neurochemical Research - Brain white matter is the means of efficient signal propagation in brain and its dysfunction is associated with many neurological disorders. We studied the effect of...     

Isolation and preliminary characterization of a casein kinase from cauliflower nuclei

A casein-type protein kinase has been isolated from cauliflower (Brassica cauliflora Gars.) nuclei and purified to a specific activity of 23,000 units/milligram of protein (1 unit is defined as the transfer of 1 picomole of ³²Pi from γ-[³²P]ATP to substrate per minute at 28 C). The enzyme has a molecular weight of approximately 39,000 as judged by sucrose density gradient sedimentation. The casein kinase requires ATP as the phosphate donor and will phosphorylate casein and phosvitin, but not histones. The enzyme activity is not affected by cAMP or cGMP. The casein kinase appears to be analogous to casein kinases described in other plant and animal systems.