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L E Orgel

Publications and source records attributed to L E Orgel.

At least 19 recordsLinked to original sources
PubMed1992

Molecular replication.

Simple replicating molecules are likely to have played a critical role in the origin of life. Recent experiments show that non-enzymatic replication is conceivable in a wide range of synthetic chemical systems. The challenge now facing these studies is how to develop information-coding systems from simple prebiotic precursors.

Base Sequence↗
PubMed1992

Crosslinking transcription factors to their recognition sequences with PtII complexes.

We have prepared phosphorothioate-containing cyclic oligodeoxynucleotides that fold into 'dumbbells' containing CRE and TRE sequences, the binding sequences for the CREB and JUN proteins, respectively. Six phosphorothioate residues were introduced into each of the recognition sequences. K2PtCl4 crosslinks CRE to CREB and TRE to JUN. The extent of crosslinking is about eight times greater than that observed with standard oligodeoxynucleotides and amounts to 30-50% of the efficiency of non-covalent association as estimated by gel-shift assays. Crosslinking is reversed by incubation with NaCN. The crosslinking reaction is specific--a dumbbell oligonucleotide with six phosphorothioate groups introduced into the Sp1 recognition sequence could not be crosslinked efficiently to CREB or JUN proteins with K2PtCl4. The binding of TRE to CREB is not strong enough for effective detection by gel-shift assays, but the TRE-CREB complex is crosslinked efficiently by K2PtCl4 and can then readily be detected.

Base Sequence↗
PubMed1991

An efficient, sequence-specific method for crosslinking complementary oligonucleotides using binuclear platinum complexes.

The binuclear PtII complexes [(trans-Pt(NH3)2Cl)2 (NH2(CH2)nNH2)]Cl2 (n = 4, 5 or 6), crosslink oligodeoxynucleotide-5'-phosphorothioates rapidly, specifically and efficiently to complementary single-stranded oligodeoxynucleotide targets. In the case that we investigated in detail, the most abundant crosslink is formed to the G residue complementary to the 5'-terminal C residue of the phosphorothioate. Less efficient crosslinking occurs to many other residues of the target. The same PtII complexes also bring about crosslinking efficiently to the polypurine tract in triple-helical DNA.

Base Composition↗
PubMed1991

Acceleration of the template-directed reactions of nucleoside 5'-phosphorimidazolides by acylation.

Nucleoside-5'-phosphorimidazolides react readily with acylating agents to give N-substituted products that are highly activated. In most cases these acylated derivatives undergo rapid hydrolysis to give nucleoside 5'-phosphates, whether or not a complementary template is present. However, guanosine 5'-phosphorimidazolide reacts with diethyl pyrocarbonate to give a derivative that oligomerizes rapidly and efficiently in the presence of polycytidylic acid and Pb2+. The reaction is complete in about 1 h, whereas the corresponding reaction in the absence of an acylating agent takes several days. However, the final yield of long oligomers is lower when diethyl pyrocarbonate is present.

Acylation↗
PubMed1991

Which 3-ribofuranosyl-substituted purine 5'-phosphates undergo template-directed oligomerization?

We have studied the oligomerization reactions of the 2-methylimidazolide derivatives of 3-isoisoguanosine 5'-phosphate (2) and 3-isoxanthosine 5'-phosphate (5) in the presence of a variety of homopolynucleotide templates. In no case did we observe a substantial template-facilitated production of long oligomers. Polyuridylic acid directed the synthesis of low molecular-weight products from both monomers. Polycytidylic acid, polyadenylic acid, polyinosinic acid, and polyguanylic acid were ineffective as templates in the systems that we investigated.

Chromatography, High Pressure Liquid↗
PubMed1991

Template-directed extension of a guanosine 5'-phosphate covalently attached to an oligodeoxycytidylate template.

We have prepared molecules in which a guanosine 5'-phosphate (pG) residue is attached to the 3' terminus of a decadeoxycytidylate (pdC)10 template via diamine linkers H2N(CH2)nNH2, n = 4-7. The pG residue acts as a primer and is extended very efficiently by incubation with activated pG derivatives to give products containing 6-9 G residues in greater than 80% yield. The detailed nature of the product distribution is discussed.

Base Sequence↗
PubMed1991

Pyrophosphate formation as the most efficient condensation reaction of activated nucleotides.

When an oligonucleotide primer pG10 is incubated with the nucleotide analogue 9-[3-hydroxy-2-(hydroxymethyl)prop-1-yl] guanine diphosphate (pGp, I) in the presence of poly(C), addition of the monomer occurs almost exclusively at the 5'-terminal phosphate rather than the 3'-terminal cis-glycol. The implications of this finding in the context of prebiotic condensation reactions are discussed.

Chromatography, High Pressure Liquid↗
PubMed1990

Optimization of the efficiency of cross-linking PtII oligonucleotide phosphorothioate complexes to complementary oligonucleotides.

We have investigated the efficiency with which PtII complexes cross-link phosphorothioates of oligonucleotides to complementary DNA targets. The A and G residues 2-5 bases downstream from the 5'-phosphorothioate group are preferred sites for cross-linking. Replacement of residues in this part of the target by T residues results in greatly decreased cross-linking when cis platinum diammine dichloride (cisPtII) or potassium platinous chloride (K2PtCl4) are used. Trans platinum diammine dichloride (transPtII) forms cross-links with T residues if A and G residues are absent from the susceptible region of the target. Oligomers containing an internal phosphorothioate group can also be linked to their templates with transPtII, but not with cisPtII or K2PtCl4. Cross-linking via an internal phosphorothioate group tends to be less efficient than cross-linking via a 5'-terminal phosphorothioate. The Sp isomers of internal phosphorothioates are cross-linked more efficiently than the Rp isomers. Preliminary experiments suggest that the efficiency of cross-linking to RNA targets will prove similar to that found for DNA targets.

Base Sequence↗
PubMed1990

Polymerization of amino acids containing nucleotide bases.

We have prepared the nucleoamino acids 1-(3'-amino,3'-carboxypropyl)uracil (3) and 9-(3'-amino,3'-carboxypropyl)adenine (4) as (L)-enantiomers and as racemic mixtures. When 3 or 4 is suspended in water and treated with N,N'-carbonyldiimidazole, peptides are formed in good yield. The products formed from the (L)-enantiomers are hydrolyzed to the monomeric amino acids by pronase. Attempts to improve the efficiency of these oligomerizations by including a polyuridylate template in the reaction mixture were not successful. Similarly, oligomers derived from the (L)-enantiomer of 3 did not act as templates to facilitate the oligomerization of 4.

Adenine↗
PubMed1989

Inhibition of DNA synthesis by cross-linking the template to platinum-thiol derivatives of complementary oligodeoxynucleotides.

Unsubstituted oligodeoxynucleotides, or oligodeoxynucleotides linked to poly-(L)-lysine, when hybridized to a 322 base long template, did not inhibit the production of full length DNA copies by the Klenow fragment of E. coli DNA polymerase I. However, synthesis was inhibited if the cysteamine derivative of the same oligomer was cross-linked to the template via PtII. Truncated products were formed by termination of DNA synthesis a small number of bases upstream from the 5'-end of the cross-linked oligomer. AMV reverse transcriptase behaved similarly but was also slightly inhibited by the hybridized oligomer or its poly-lysine derivative.

Base Composition↗
PubMed1989

Reaction on alternating GC oligonucleotide templates.

The condensation reactions of activated nucleotides, ImpN or 2-MeImpN, with the self-complementary ribo-octanucleotide GCGCGCGC or with the partially self-complementary heptanucleotide GCGCGCG were studied. The template-directed reaction of 2-MeImpC with the heptamer yields the 3'-5' octamer as the main product. All other reactions yield 2'-5'-linked octamers and pyrophosphates as major products. Surprisingly, 2-MeImpG facilitates the reaction of 2-MeImpC with the heptamer. Procedures for the analysis by gel electrophoresis of the oligomeric products obtained in reactions of this kind are described.

Autoradiography↗
PubMed1989

Polymerization of a monomeric guanosine derivative in a hydrogen- bonded aggregate.

The adduct IIa, in which glycine is linked to the 3'-amino group of 3'-deoxyguanosine-5'-phosphate, condenses very efficiently in aqueous solution when treated with a water-soluble carbodiimide to give long oligomeric products. The corresponding cytidine derivative IIb yields a complex mixture of very short oligomers. We believe that the efficient condensation reaction occurs in a hydrogen-bonded tetrahelical aggregate of a type that is known to form with many guanosine derivatives.

Amino Acids↗
PubMed1989

The origin of polynucleotide-directed protein synthesis.

If protein synthesis evolved in an RNA world it was probably preceded by simpler processes by means of which interaction with amino acids conferred selective advantage on replicating RNA molecules. It is suggested that, at first, the simple attachment of amino acids to the 2'(3')-termini of RNA templates favored initiation of replication at the end of the template rather than at internal positions. The second stage in the evolution of protein synthesis would probably have been the association of pairs of charged RNA adaptors in such a way as to favor noncoded formation of peptides. Only after this process had become efficient could coded synthesis have begun.

Adenosine Monophosphate↗
PubMed1989

Replacement of the 3'-CH group by nitrogen in the carbocyclic analogue of thymidine.

We have prepared (4R)-4-thyminyl-D-prolinol, an analogue of 3'-deoxythymidine in which the sugar has been replaced by D-prolinol. This strongly basic secondary amine has been converted to the corresponding hydroxylamine, an analogue of either thymidine or 2'-deoxyxylofuranosylthymine. We have also synthesized a number of simple derivatives of the amine for testing in vitro activity against herpes simplex 1 (HSV-1), human immunodeficiency virus 1 (HIV-1), and a panel of human tumor cell lines. Among these compounds, the hydroxylamine 12 proved active against the human tumor cell lines of breast, colon, and lung origin, with IC50 values of 0.08, 14.02, and 6.91 microM, respectively.

Antineoplastic Agents↗