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25.
RNA pseudoknots. Stability and loop size requirements. 总被引:7,自引:0,他引:7
The effects of ionic conditions, loop size and loop sequence on the formation of pseudoknots by RNA oligonucleotides have been investigated using biochemical and biophysical methods. An oligonucleotide with the sequence 5' GCGAUUUCUGACCGCUUUUUUGUCAG 3' and oligonucleotides with variations in the sequences of the two loop regions, denoted by bold face type, were studied. Each sequence with the potential to form a pseudoknot can also form two stable hairpins. The pseudoknot structure is stabilized relative to the hairpins by addition of Mg2+. Even in the presence of Mg2+, the pseudoknots formed by the sequences investigated are only marginally more stable (1.5 to 2 kcal mol-1 in free energy at 37 degrees C) than either of the constituent hairpins. The pseudoknot structure is the stable conformation in the presence of Mg2+ when the first loop region is at least three nucleotides and the second is at least four nucleotides. Further deletion of nucleotides from the loop regions stabilizes possible hairpin structures relative to the pseudoknot and equilibria among secondary and tertiary structures result. 相似文献
26.
Matrix attachment regions (MARs) are thought to participate in the organization and segregation of independent chromosomal loop domains. Although there are several reports on the action of MARs in the context of heterologous genes, information is more limited on the role of MARs associated with plant genes. Transgenic studies suggest that the upstream, intron and downstream regions of the developmentally regulated heat shock cognate 80 gene (HSC80) of tomato participate in chromatin organization. In this study, we tested the in vitro affinity of the HSC80 gene to chromosomal scaffolds prepared from shoot apices of tomato. We found that a 1.5 kb upstream region and a 1.4 kb downstream region, but not the intron region, are MARs. These MARs interact with tomato and pea scaffolds and bind regardless of the expression status of HSC80 in the tissue from which the nuclei were isolated. Comparison to two known yeast MARs ARS1 and CENIII, showed that the HSC80 5MAR binds more avidly to tomato scaffolds than ARS1, while no binding of CENIII was observed. Competition binding between the two HSC80 MARs indicated that the 5 MAR can outcompete the 3 MAR and not vice versa. Last, we observed that the interaction of the 3 MAR with the scaffold could result in an electrophoretic mobility shift resistant to SDS, protease, and phenol treatment. In conclusion, MARs whose binding properties can be clearly differentiated are closely flanking the HSC80 gene. The discovery of MARs in regions which have a distinct function in HSC80 transgenes but not in transient expression assays, is consistent with a chromosomal scaffold role in HSC80 gene regulation. 相似文献
27.
Dr. Luca Martire 《Facies》1996,35(1):209-236
Summary The red, pelagic limestones of the Rosso Ammonitico Veronese (Upper Bajocian-Tithonian) of the Altopiano di Asiago area can
be subdivided into eight facies. They differ from each other in structure (bedding style, presence and type of nodularity)
and texture (nature of components, grain-vs mud-support, compactional features). Several discontinuities could be recognized,
based on sedimentological or biostratigraphic evidence. In the context of a drowned platform, where sediments essentially
consist of skeletal remains of both planktonic and benthic organism, the different facies are interpreted as reflecting a
varying influence of currents on the winnowing of micrite and on triggering early cementation. Early cementation in turn,
controlled the patterns of bioturbation and the response of sediments to later compaction and pressure-dissolution. At times,
microbial mats, of unidentified nature, were important in trapping and binding sediment, giving rise to early lithified nodules
and layers of stromatolitic aspect.
The Rosso Ammonitico Veronese can be subdivided into three units: lower Rosso Ammonitico (RAI: Upper Bajocian-Lower Callovian),
middle Rosso Ammonitico (RAM: Upper Callovian-Middle Oxfordian), and upper Rosso Ammonitico (RAS: Lower Kimmeridgian-Tithonian).
Frequent ammonite moulds allow the precise dating of the base and top of each unit, and the documentation of facies heteropies
and hiatusses in the more fossiliferous RAS. The lower unit (RAM) is massive and essentially nodular; the middle unit (RAM)
is well bedded, non-nodular, and cherty; the upper unit (RAS) is richer in clay and typically nodular. The RAI and the RAS
are present everywhere, though significant facies and thickness changes affect particularly the RAS; the RAM is much more
variable, ranging from 0 to 10 metres. These variations, that may be gradual or abrupt, are inter-preted as the result of
Middle-Late Callovian block-faulting which generated an irregular sea floor topography where the swells were more exposed
to currents that continuously removed sediments, inducing long-lasting periods of nondeposition. Sediments preferentially
accumulated in the adjacent lows. A confirmation of this hypothesis is provided by evidence of synsedimentary tectonics, described
for the first time in the Rosso Ammonitico Veronese. Neptunian dykes, both vertical and horizontal, are developed at the top
of the RAI and are filled with laminated sediments or collapse breccias. Glides of metre-size blocks and slumps are present
at the top of the RAI and at the base of the RAM, respectively. Cm-thick layers of mud supported breccias are intercalated
in the upper part of the RAI and within the RAM: they are interpreted as seismites. All these features document a tensional
regime that generated fractures in more or less lithified sediments and failure along steep fault scarps or gently dipping
slopes of tilted fault blocks. Recognition of this Callovian-Oxfordian tectonic activity shows that, after the Bajocian drowning,
the Trento Plateau did not simply experience a uniform and general foundering: a small-scale block-faulting was still active
and affected the pattern of facies distribution. 相似文献
28.
Pierre Taberlet Luca Fumagalli Jacques Hausser 《Evolution; international journal of organic evolution》1994,48(3):623-636
The shrews of the Sorex araneus group have undergone a spectacular chromosome evolution. The karyotype of Sorex granarius is generally considered ancestral to those of Sorex coronatus and S. araneus. However, a sequence of 777 base pairs of the cytochrome b gene of the mitochondrial DNA (mtDNA) produces a quite different picture: S. granarius is closely related to the populations of S. araneus from the Pyrenees and from the northwestern Alps, whereas S. coronatus and S. araneus from Italy and the southern Alps represent two well-separated lineages. It is suggested that mtDNA and chromosomal evolution are in this case largely independant processes. Whereas mtDNA haplotypes are closely linked to the geographical history of the populations, chromosomal mutations were probably transmitted from one population to another. Available data suggest that the impressive chromosome polymorphism of this group is quite a recent phenomenon. 相似文献
29.
Acetaldehyde production in Saccharomyces cerevisiae wine yeasts 总被引:1,自引:0,他引:1
Patrizia Romano Giovanna Suzzi Luca Turbanti Mario Polsinelli 《FEMS microbiology letters》1994,118(3):213-218
Abstract Eighty-six strains of Saccharomyces cerevisiae were investigated for their ability to produce acetaldehyde in synthetic medium and in grape must. Acetaldehyde production did not differ significantly between the two media, ranging from a few mg/l to about 60 mg/l, and was found to be a strain characteristic. The fermentation temperature of 30°C considerably increased the acetaldehyde produced. This study allowed us to assign the strains to different phenotypes: low, medium and high acetaldehyde producers. The low and high phenotypes differed considerably also in the production of acetic acid, acetoin and higher alcohols and can be useful for studying acetaldehyde production in S. cerevisiae , both from the technological and genetic point of view. 相似文献