Lipid-assisted Synthesis of RNA-like Polymers from Mononucleotides

A fundamental problem in research on the origin of life is the process by which polymers capable of catalysis and replication were produced on the early Earth. Here we show that RNA-like polymers can be synthesized non-enzymatically from mononucleotides in lipid environments. The RNA-like polymers were initially identified by nanopore analysis, a technique with single molecule sensitivity. To our knowledge, this is the first such application of a nanopore instrument to detect RNA synthesis under simulated prebiotic conditions. The synthesis of the RNA-like polymers was confirmed by standard methods of enzymatic end labeling followed by gel electrophoresis. Chemical activation of the mononucleotides is not required. Instead, synthesis of phosphodiester bonds is driven by the chemical potential of fluctuating anhydrous and hydrated conditions, with heat providing activation energy during dehydration. In the final hydration step, the RNA-like polymer is encapsulated within lipid vesicles. This process provides a laboratory model of an early stage of evolution toward an RNA World.     

Synthesis of messenger RNA-like molecules in isolated myeloma nuclei.

Nuclei isolated from mouse myeloma cells grown in tissue culture are capable of synthesizing RNA for prolonged periods of time. Addition of cytoplasmic extracts to the system stimulates slightly the rate and prolongs the time of synthesis. As judges by sedimentation in SDS and in formamide gradients, the size of the RNA synthesized is heterogeneous from smaller than 10S to larger than 45S, thus resembling in vivo made RNA. The characteristics of some of the RNA are in keeping with those expected to be for mRNA. Fifty percent of the RNA synthesis is sensitive to alpha-amanitin. After an incubation of two hours in the absence of alpha-amanitin about 10 percent of the newly synthesized RNA is found outside of the nuclei; it sediments with a broad distribution at 18S. A considerable fraction of the RNA that is released from nuclei in vitro can promote the formation of polyribosomes, and contains molecules that are polyadenylated and "capped".     

Nucleosides and nucleotides. 232. Synthesis of 2'-C-methyl-4'-thiocytidine: unexpected anomerization of the 2'-keto-4'-thionucleoside precursor

The synthesis of 2'-C-methyl-4'-thiocytidine (16) is described. Since the 2'-keto-4'-thiocytidine derivative 2beta unexpectedly isomerized to 2alpha and the methylation of 2beta proceeded predominantly from the less hindered alpha-face to give 7, the desired product 16 was synthesized via the Pummerer reaction of the sulfoxide 14 and N4-benzoylcytosine.     

RNA-like conformational properties of a synthetic DNA poly(dA-dU).poly(dA-dU)

Differences in the circular dichroism of poly(dA-dT).poly(dA-dT) and poly(dA-dU).poly(dA-dU) and in its temperature induced changes are reported. A comparison to the data obtained with DNA and RNA indicates that an absence of thymine methyl groups in the polynucleotide results in promoting its RNA-like conformational properties. However, poly(dA-dU).poly(dA-dU) is not an A-DNA type of double helix.     

Evolution of complexity in RNA-like replicator systems

Background  

The evolution of complexity is among the most important questions in biology. The evolution of complexity is often observed as the increase of genetic information or that of the organizational complexity of a system. It is well recognized that the formation of biological organization – be it of molecules or ecosystems – is ultimately instructed by the genetic information, whereas it is also true that the genetic information is functional only in the context of the organization. Therefore, to obtain a more complete picture of the evolution of complexity, we must study the evolution of both information and organization.     

Structure and unexpected chiroptical properties of chiral 4-pyrrolidinyl substituted 2(5H)-furanones

Planar 2(5H)-furanones substituted at C4 with a chiral pyrrolidinyl group show CD spectra which are apparently due to the distortion of the C4-N1 bond of sp2 character from the plane defined by the 2(5H)-furanone ring atoms and/or due to the presence of substituents in the pyrrolidine ring. This is a new, previously not encountered structural factor determining the chiroptical properties of 2(5H)-furanones and emerging from the analysis of X-ray diffraction data and quantum mechanical DFT computations. In the presence of a C5 pseudoaxial substituent in the furanone ring, the sign of the furanone n-pi* and pi-pi* transition Cotton effects is determined primarily by the previously postulated allylic helicity rule.     

Synthesis and SAR of a novel metabotropic glutamate receptor 4 (mGlu4) antagonist: unexpected 'molecular switch' from a closely related mGlu4 positive allosteric modulator

Herein we report the discovery and SAR of a novel antagonist of metabotropic glutamate receptor 4 (mGlu(4)). The antagonist was discovered via a molecular switch from a closely related mGlu(4) positive allosteric modulator (PAM). This antagonist (VU0448383) displays an IC(50) value of 8.2±0.4 μM and inhibits an EC(80) glutamate response by 63.1±6.6%.     

Lipid traffic: Osh4p makes an unexpected exchange

A new study in this issue (De Saint-Jean et al. 2011. J. Cell Biol. http://dx.doi.org/jcb.201104062) reveals that the sterol transfer protein Osh4p can also transport the signaling phospholipid phosphatidylinositol 4-phosphate (PI(4)P), which binds to the same site in Osh4p as sterol. This finding helps explain some previously published studies and also indicates that lipid/sterol exchange could contribute to establishing a sterol gradient in cells.     

A new enkephalin analogue: trans-4-hydroxycinnamoyl-glycyl-glycyl-phenylalanyl-leucine. Synthesis and biological properties

A new analogue of the leucine-enkephalin in which the N-terminal tyrosine has been replaced by trans-4-hydroxycinnamic acid, has been synthetized by liquid-phase coupling methods. The central cardiovascular effects of this analogue were investigated and the results discussed.     

Synthesis and antiviral properties of novel indole-based thiosemicarbazides and 4-thiazolidinones

A novel series of indolylthiosemicarbazides (6a–6g) and their cyclization products, 4-thiazolidinones (7a–7g), have been designed, synthesized and evaluated, in vitro, for their antiviral activity against a wide range of DNA and RNA viruses. Compounds 6a, 6b, 6c and 6d exhibited notable antiviral activity against Coxsackie B4 virus, at EC₅₀ values ranging from 0.4 to 2.1 μg/mL. The selectivity index (ratio of cytotoxic to antivirally effective concentration) values of these compounds were between 9 and 56. Besides, 6b, 6c and 6d also inhibited the replication of two other RNA viruses, Sindbis virus and respiratory syncytial virus, although these EC₅₀ values were higher compared to those noted for Coxsackie B4 virus. The SAR analysis indicated that keeping the free thiosemicarbazide moiety is crucial to obtain this antiviral activity, since the cyclization products (7a–7g) did not produce any antiviral effect.     

Association of hY4 pseudogenes with Alu repeats and abundance of hY RNA-like sequences in the human genome.

Three loci having homology with the small human cytoplasmic RNA, hY4, were isolated from human genomic DNA libraries and sequenced. Each sequence contains dispersed mismatches as compared with hY4 RNA, is followed by an A-rich or A + T-rich sequence, and is bordered by direct repeats. Each of these loci, therefore, appears to constitute a small RNA class-III pseudogene. Surprisingly, two of the three loci are associated with Alu repeats. In the hY4.B7 locus, the hY4 sequence has integrated into the tail of an Alu element and in the hY4.F2 locus, an Alu sequence has inserted into the hY4 tail, confirming that A-rich tracts are preferential targets for retroposition. In addition, Southern blots with probes for each of the four hY RNAs indicate that hY RNA-like sequences are abundant in the human genome.     

TBAF and cellulose esters: unexpected deacylation with unexpected regioselectivity

Tetrabutylammonium fluoride has been found to catalyze the deacylation of cellulose esters. More surprisingly, the deacylation is highly regioselective. Even more remarkably, in contrast with the C-6 regioselectivity of other reactions of cellulose and its derivatives, this deacylation shows substantial selectivity for the removal of the acyl groups from the esters of the secondary alcohols at C-2 and C-3, affording cellulose-6-O-esters with high regioselectivity by a simple one-step process employing no protective groups.