The structure of the 5' domain of yeast 18S rRNA has been probed by dimethyl sulfate (DMS), either in "native" deproteinized molecules or in the 40S ribosomal subunits. DMS-reacted RNA has been used ...as a template for reverse transcription and a large number of reactive sites, corresponding to all types of bases have been mapped by a primer extension procedure, taking advantage of blocks in cDNA elongation immediately upstream from bases methylated at atom positions involved in the base-pair recognition of the template. Since the same atom positions are protected from DMS in base-paired nucleotides, the secondary structure status of each nucleotide can be directly assessed in this procedure, thus allowing to evaluate the potential contribution of proteins in modulating subunit rRNA conformation. While the DMS probing of deproteinized rRNA confirms a number of helical stems predicted by phylogenetic comparisons, it is remarkable that a few additional base-pairings, while proven by the comparative analysis, appear to require the presence of the bound ribosomal subunit proteins to be stabilized.
The structure of the 5' domain of yeast 18S rRNA has been probed by dimethyl sulfate (DMS), either in "native" deproteinized molecules or in the 4OS ribosomal subunits. DMS-reacted RNA has been used ...as a template for reverse transcription and a large number of reactive sites, corresponding to all types of bases have been mapped by a primer extension procedure, taking advantage of blocks in cDNA elongation inmediately upstream from bases methylated at atom position involved in the base-pair recognition of the template. Since the same atom positions are protected from DMS in base-paired nucleotides, the secondary structure status of each nucleotide can be directly assessed in this procedure, thus allowing to evaluate the potential contribution of proteins in modulating subunit rRNA conformation.
Multiprocessing Fleckenstein, Charles J.; Gill, D.H.; Hemmendinger, David ...
Advances In Computers,
1992, Letnik:
35
Book Chapter, Journal Article
Recenzirano
The chapter gives an overview of multiprocessor machines, attempts to survey the state of the art in multiprocessing, and provides direction for future work. An overview of parallel programming is ...presented and includes a view of the functional language FP. A comparison of two memory models, shared and distributed, is presented. The chapter extends the number of memory models by considering a hybrid approach: distributed shared memory. Techniques for supporting this model are discussed. The Orca model of automatic distribution of data structures and the Linda model of distributed data structures are attractive. Despite the evident merits of very high-level declarative logic and functional languages, the von Neumann model survives in the multiprocessor environment. The chapter examines the use of compiler support to make a program execute in parallel. It particularly considers the trade-offs between the size of each process and the amount of communication that occurs among the processes. Parallel discrete event simulation (PDES) represents another approach to studying the parallelization of general purpose applications as well as providing an approach to speeding up existing sequential simulations that may take hours or days to run. The chapter addresses the problems of maintaining the simulation clock in a distributed environment. The time warp mechanism and variations on that scheme are presented. Much work remains to take full advantage of the power of multiprocessing. The promising approaches, which have been mentioned in the chapter, in the coming years, will allow software development to keep pace with hardware development.
Hirudin (HIR), a polypeptide of 65 aminoacids, is the most potent natural inhibitor of coagulation by forming rapidly a very stable and specific non covalent 1:1 complex with α-thrombin, independent ...of antithrombin III. Although natural HIR has in vivo anticoagulant and antithrombotic properties, its limited availability for large scale purification has prevented further clinical testing and potential use; this can now be solved by recombinant DNA technology. We have previously reported the cloning and expression of a cDNA encoding one variant (called HV-2) of Hirudo medicinalis HIR (Proc. Natl. Acad. Sci. USA. 1986, 83, 1084-1088). The main factors responsible for venous thrombosis are stasis and thrombin generation secondary to tissue factor liberation from vascular cells and monocytes by injury, endotoxin, interleukin-1 or cachectin and the subsequent activation and circulation of activated clotting factors. We have studied the antithrombotic properties of recombinant HIR, HV-2, in a rat experiemental model of venous thrombosis. HV-2 was expressed in yeast, extracted from culture supernatant and purified by HPLC. Pure HV-2 had an isoleucine NH
2
-terminus and a specific activity of 13000 ATU/mg.30 male Wistar rats (225-300g) were anesthetized with pentobarbital. At time t (0 min) an i.v. (penis) injection of 0.4 ml of saline or HV-2 (2000 to 8000 ATU/kg) was given, followed at t (5min) by 25 mg/kg tissue factor (Thromboplastin C, Dade) i.v. ; 10 s later stasis of the exposed vena cava between 2 sutures 0.7 cm apart and at t (15 min) removal, blotting, fixation and weighing of the thrombus. Linear regression analysis showed a correlation (r=0.99) between the dose of HV-2 and thrombus weight and a calculated IC
50
= 3000 ATU/kg. Total inhibition of thrombus formation was seen after injection of 6000 ATU/kg HV-2 and lasted up to 15 min of circulation, HV-2 being completely eliminated from blood in 60 min and accumulated in the kidneys as shown by gamma imaging with
131
I-HV-2. In conclusion, the recombinant HIR HV-2 is a potent immediate antithrombin which inhibits venous thrombosis induced by tissue factor and stasis.
