Hans Günter Gassen

On the covalent binding of mRNA models to the part of the 16 S RNA which is located in the mrna binding site of the 30 S ribosome

Summary The oligonucleotide U-U-| 3 H|U-(nh 2 ) 2 U as a mRNA model was bound covalently to the 16 S RNA via the bifunctional guanosine-specific reagent p-chlorocarboxyphenylglyoxal. Since the ribosomes labeled with the oligonucleotide stimulated the binding of Phe-tRNA, it is concluded, that the probe reacted specifically with a guanosine of the 16 S RNA which forms the mRNA binding site of the 30 S ribosome. The binding of the probe was inhibited by poly(U), but stimulated by the presence of Phe-tRNA. 83 % of the radioactivity was found in the 16 S RNA of the ribosomal subunit. After digesting the 16 S RNA with ribonuclease T1 and separating the oligonucleotides formed by gel electrophoresis, the radioactive labeled material was mainly found in one distinct band.

Ligand-Induced Conformational Changes in Ribonucleic Acids

Publisher Summary This chapter discusses the ligand-induced conformational changes in ribonucleic acids (RNAs). This chapter also discusses the newer results on induced structural changes in transfer ribonucleic acids (tRNA), focusing on codon-induced changes, and then emphasize a new aspect— namely, the evidence for allosteric conformational changes in nucleic acids. Transfer RNAs are recognized by two different classes of proteins: those that bind only to their cognate tRNAs (like aminoacyl synthetases) and the elongation factor EF-Tu, that form complexes with all aminoacylated tRNAs. Transfer RNA (tRNA) may exist as both aminoacyl- or peptidyl-tRNA and several isoacceptor tRNAs may exist for only one amino acid. Besides a complicated tertiary structure and many modified nucleosides, there is a third way to ease the correlation of structure, with the many tRNA functions. Like proteins, tRNA may undergo induced structural transitions and there may be one defined tRNA conformation for every biochemical process. The chapter also discusses induced allosteric conformational changes in tRNA.

5-substituents in the uridine moiety and their effect on the conformation of ApU-type dinucleoside phosphates

The ApU analogues ApT, Apcl5U, Apbr5U, Apa5U and Apno5(2)U were synthesized with the aid of ribonuclease U2 starting from 2,3-cyclic Ap and the respective uridine derivatives. For these compounds the ultraviolet data, the difference spectra, the hypochromism and the temperature dependence of the CD spectra are reported. The dimerisation shifts of the pyrimidine protons which were obtained from the 100 MHz PMR spectra confirm the optical results. The influence of the substituents in the 5 position of the uracil ring on base-base interaction and the conformation of the dinucleoside phosphates is discussed with respect to the van der Waals radii and the electronic effects of these groups. As calculated from the hypochromism the dinucleoside phosphates can be arranged according to decreasing base-base interaction: Apno5(2)U greater than Apbr5U approximately ApT greater than Apcl5U greater than ApU greater than Apa5U.

DIE BLUT-HIRN-SCHRANKE : EINE BESONDERHEIT DES CEREBRALEN MIKROZIRKULATIONSSYSTEMS

The blood-brain barrier, located in cerebral capillaries, guarantees a supply of glucose to neuroactive areals and protects against the penetration of harmful compounds. From the pharmaceutical point of view the limitation in transport is a problem: therapeutically effective substances are not able to reach the brain via the bloodstream. Blood-brain barrier research contributes to the understanding of the cerebral microcirculatory system.

Codon-induced Structural Transitions in tRNA

With the structure of an RNA known in one conformation, one may ask whether this RNA molecule may change its conformation during its biological function (Kurland et al. 1975). Such could occur during aminoacylation (Dvorak et al. 1976Dvorak et al. 1978), in the formation of the ternary complex aminoacyl-tRNA · EF-Tu · GTP (Pingoud et al. 1978), or during the codon-directed binding of aminoacyl-tRNA to the ribosome (Schwarz et al. 1976; Schwarz and Gassen 1977). (EF-Tu is elongation factor Tu.) In this paper we restrict ourselves to structural transitions that occur during the codon-directed binding of either initiator or elongator tRNA to the ribosome. Conformational changes in the anticodon-loop region of the tRNA were postulated by Woese (1970). In an extension of the Fuller and Hodgson (1967) model, he proposed a transition between the 3′-stacked and the 5′-stacked conformation as a basic mechanism for mRNA translocation. Recently, Urbanke and Maass (1978) measured the temperature dependence of the fluorescence of the “Y-base” in yeast tRNA phe . A slow structural transition characterized by a monomolecular all-or-none effect was found. These authors, too, discuss as a possible explanation for their data a transition from the 3′-stacked (the more stable one) to the 5′-stacked anticodon structure (Urbanke and Maass 1978). Similar experiments were performed earlier by Yoon et al. (1975), who arrived at similar conclusions. Although C32 and U33 are not available for binding in the crystal lattice of tRNA phe , UUCA and the pentamer UUCAG are bound more effectively to the anticodon region of the tRNA than...