To survive, an informational macromolecule must solve the major problem set by its very polymeric nature: instability. This is especially true in prebiotic terms because of the presumed initial absence of protective structures (proteins, lipids, etc.). We have analyzed the stability of the -glycosidic and of the 3-and 5-phosphoester bonds in both deoxy monomers and deoxy oligomers under a large set of conditions. The results show a strong dependence of the relative stability of these bonds on the physico-chemical environment. A set of conditions has been identified in which the stability of polymers becomes comparable with that of the precursor monomers. In certain instances the stability of the 5-phosphoester bond is even higher in the polymer than in the mononucleotide.If life on this planet had an early start as it seems (1-8), several conditions had to be satisfied at the same time: abundance of the starting biogenic materials, formation of precursors based on simple chemical processes, and simultaneous (or quasi so) presence of the building blocks to be used for the assembling of informational molecules. We have observed (Refs. 9 -11 and references therein) that the one-carbon compound formamide is an highly versatile building block for the synthetic processes yielding all the necessary precursor nucleic bases. In terms of its possible role in allowing or favoring the formation of informational nucleic polymers, formamide chemistry also provides a possible solution to the lack of reactivity between ribose/deoxyribose with bases through a formose-like reaction yielding acyclonucleosides (10). The reported activity of formamide as activator of transphosphorylation (see "Discussion") provides additional possible relevance to its role in prebiotic reactions leading to pre-genetic informational polymers. The plausibility of its prebiotic role is related to (i) its presence in interstellar medium, in comets and asteroids (12), hence on early Earth; (ii) the ease of its formation by hydrolysis of HCN and its stability in liquid form over a wide range of temperatures (2.5-210°C), thus favoring its concentration from dilute aqueous solutions; and (iii) the above mentioned catalyst-induced wealth of nucleic precursors.The question arises as to whether the physico-chemical conditions (moderately high temperature and varying concentration of formamide in water) allowing active synthesis and potentially leading to polymerization favor or impair the survival of the polymerized materials. In reconstructing the passage from monomers to the information-bearing polymers that we know at present, two major pieces of the mosaic are markedly missing: the knowledge of the mechanisms leading to the formation of the -glycosidic and of the 3Ј-5Ј phosphodiester bonds and, once the polymer had been formed, the physico-chemical reason(s) leading to its very survival as a polymer. In other words, which is the Darwinian selective advantage that overcame the intrinsically higher instability of the polymeric form?The analysis presented h...
Thialysine can be utilized for growth by a wild type K12 strain of E. coli. It is incorporated into proteins in substitution and in competition with lysine; up to 17% of protein lysine can be substituted by thialysine. Nevertheless the presence of thialysine in the culture medium gives rise to an inhibition of cell growth rate. This effect has been correlated to the inhibition of protein synthesis rate by thialysine and to the extent of protein lysine substitution by the analog. On the other hand this substitution does not affect cell viability.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.