RESUMO
The electron microscopic data and the CD spectra of poly(G) have shown that the transition of a freeze-dried preparation of poly(G) from a "metastable" to a "stable" form is the transition of the four-stranded poly(G) from the globular form to the linear one. The observed phenomenon of the formation of long four-stranded poly(G) fibers (4--5 nm in diameter and 200-2000 nm in length) is suggested to be a result of a joint of the initial poly(G) molecules (50--80 nm in length) due to noncovalent binding ("sticking") of their free one-, double- or three-stranded ends. This phenomenon has permitted us not only to compare the thickness of low molecular weight poly (G) preparations under different conditions but to observe directly the existence of a large number of double-stranded (2--3 nm in diameter) regions ("defects") in four -stranded poly(G) fibers. The data obtained have shown that under certain conditions (high temperature, low pH, etc.) the four-stranded poly(G) fibers break down with the formation of two-stranded poly(G) fibers whose hydrogen bond systems depend on the conditions of their formation.
Assuntos
Poli G , Polirribonucleotídeos , Fenômenos Químicos , Química , Dicroísmo Circular , Liofilização , Concentração de Íons de Hidrogênio , Microscopia Eletrônica , Conformação de Ácido Nucleico , Soluções , Temperatura , ÁguaRESUMO
The kinetic of 1H leads to 3H exchange between water and C(8)H-groups of the guanylic residues in poly(G) . poly(C) and poly(dG) . poly(dC) was investigated within the temperature range from 30 to 90 degrees in 0.5 M NaCl (pH 7.2). It was shown that the exchange in freshly dissolved preparations at temperatures lower than 50 degrees proceeds faster than that in the case of GMP. According to the ylide mechanism of the exchange reaction the observed acceleration of the exchange is considered as a consequence of associates formation in poly(G) . poly(c) and poly(dG) . poly(dC) solutions at temperatures lower than 50 degrees. Associates are stabilized by intermolecular hydrogen bonds in which N(7) atoms of guanylic residues take part. The increase of the temperature is accompanied by gradual disappearance of the exchange acceleration. The retardation of exchange, which is characteristic of most non-associated double-stranded polynucleotides and nucleic acids is observed at the temperatures above 60 degrees. The retardation points to thermal destruction of the associates at temperatures higher than 50 degrees. The associates which are characterized by ordered structure including several "side by side" arranged double-stranded molecules were observed by electron microscopy. The addition of EDTA to solutions as well as the increase of temperature leads to destruction of the associates whereas the addition of Mg2+ makes the associates more stable.
