The RNA-binding domain of ribosomal protein L11 recognizes an rRNA tertiary structure stabilized by both thiostrepton and magnesium ion.

Antibiotics that inhibit ribosomal function may do so by one of several mechanisms, including the induction of incorrect RNA folding or prevention of protein and/or RNA conformational transitions. Thiostrepton, which binds to the 'GTPase center' of the large subunit, has been postulated to prevent conformational changes in either the L11 protein or rRNA to which it binds. Scintillation proximity assays designed to look at the binding of the L11 C-terminal RNA-binding domain to a 23S ribosomal RNA (rRNA) fragment, as well as the ability of thiostrepton to induce that binding, were used to demonstrate the role of Mg(2+), L11 and thio-strepton in the formation and maintenance of the rRNA fragment tertiary structure. Experiments using these assays with both an Escherichia coli rRNA fragment and a thermostable variant of that RNA show that Mg(2+), L11 and thiostrepton all induce the RNA to fold to an essentially identical tertiary structure.

Structure-activity relationships of novel 2-substituted quinazoline antibacterial agents.

High-throughput screening of in-house compound libraries led to the discovery of a novel antibacterial agent, compound 1 (MIC: 12-25 microM against S. pyogenes). In an effort to improve the activity of this active compound, a series of 2-substituted quinazolines was synthesized and evaluated in several antibacterial assays. One such compound (22) displayed improved broad-spectrum antibacterial activity against a variety of bacterial strains. This molecule also inhibited transcription/translation of bacterial RNA, suggesting a mechanism for its antibiotic effects. Structure-activity relationship studies of 22 led to the synthesis of another 24 compounds. Although some of these molecules were found to be active in bacterial growth assays, none were as potent as 22. Compound 22 was tested for its ability to cure a systemic K. pneumonia infection in the mouse and displayed moderate effects compared with a control antibiotic, gentamycin.

Inhibition of NF-kappa B specific transcriptional activation by PNA strand invasion.

Peptide nucleic acid (PNA) strand invasion offers an attractive alternative to DNA oligonucleotide directed triplex formation as a potential tool for gene inhibition. Peptide nucleic acid has been shown to interact with duplex DNA in a process which involves strand invasion of the duplex and binding of one of the DNA strands with two PNA oligomers. By blocking the interaction of a transcription factor with 5' regulatory sequences, PNA might specifically down-regulate gene activity. Here we demonstrate that PNA is capable of specifically blocking interaction of the transcription factor NF-kappa B with the IL2-R alpha NF kappa-B binding site in vitro. We further demonstrate that this interaction is sufficient to prevent transcriptional transactivation both in vitro and when transfected into cells in culture.

Evaluation of pyrimidine PNA binding to ssDNA targets from nonequilibrium melting experiments.

Slow kinetics of homopyrimidine PNA binding to single stranded DNA and RNA targets is manifested in significant hysteresis in thermal UV absorption experiments. We have compared temperatures of dissociation (Tdis) and reassociation (Tass) for triplexes formed by DNA and single or bis PNAs with K50 derived from gel mobility experiments. Results indicated there was no correlation between Tdis and K50 while reasonable correlation between Tass and K50 was found. This correlation enabled use of easy thermal UV absorption experiments for evaluation of PNA binding to DNA/RNA targets.

Investigation of some properties of oligodeoxynucleotides containing 4'-thio-2'-deoxynucleotides: duplex hybridization and nuclease sensitivity.

The thermal stabilities of the duplexes formed between 4'-thio-modified oligodeoxynucleotides and their DNA and RNA complementary strands were determined and compared with those of the corresponding unmodified oligodeoxynucleotides. A 16mer oligodeoxynucleotide containing 10 contiguous 4'-thiothymidylate modifications formed a less stable duplex with the DNA target (deltaTm/modification -1.0 degrees C) than the corresponding unmodified oligodeoxynucleotide. However, when the same oligodeoxynucleotide was bound to the corresponding RNA target, a small increase in Tm was observed (deltaTm/modification +0.16 degrees C) when compared with the unmodified duplex. A study to identify the specificity of an oligodeoxynucleotide containing a 4'-thiothymidylate modification when forming a duplex with DNA or RNA containing a single mismatch opposite the modification found the resulting Tms to be almost identical to the wild-type duplexes, demonstrating that the 4'-thio-modification in oligodeoxynucleotides has no deleterious effect on specificity. The nuclease stability of 4'-thio-modified oligodeoxynucleotides was examined using snake venom phosphodiesterase (SVPD) and nuclease S1. No significant resistance to degradation by the exonuclease SVPD was observed when compared with the corresponding unmodified oligodeoxynucleotide. However, 4'-thio-modified oligodeoxynucleotides were found to be highly resistant to degradation by the endonuclease S1. It was also demonstrated that 4'-thio-modified oligodeoxynucleotides elicit Escherichia coli RNase H hydrolysis of the RNA target only at high enzyme concentration.

Characterization of fully 2'-modified oligoribonucleotide hetero- and homoduplex hybridization and nuclease sensitivity.

The nuclease stability and melting temperatures (Tm) were compared for fully modified oligoribonucleotide sequences containing 2'-fluoro, 2'-O-methyl, 2'-O-propyl and 2'-O-pentyl nucleotides. Duplexes formed between 2' modified oligoribonucleotides and RNA have typical A-form geometry as observed by circular dichroism spectroscopy. Modifications, with the exception of 2'-O-pentyl, were observed to increase the Tm of duplexes formed with complementary RNA. Modified homoduplexes showed significantly higher Tms, with the following Tm order: 2'-fluoro:2'fluoro > 2'-O-propyl:2'-O-propyl > 2'-O-methyl:2'-O- methyl > RNA:RNA > DNA:DNA. The nuclease stability of 2'-modified oligoribonucleotides was examined using snake venom phosphodiesterase (SVPD) and nuclease S1. The stability imparted by 2' modifications was observed to correlate with the size of the modification. An additional level of nuclease stability was present in oligoribonucleotides having the potential for forming secondary structure, but only for 2' modified oligoribonucleotides and not for 2'-deoxy oligoribonucleotides.