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J Pilet

Publications and source records attributed to J Pilet.

11 recordsLinked to original sources
PubMed1982

The B reversible Z transition of poly(dI-br5dC).poly(dI-br5dC). A quantitative description of the Z form dynamic structure.

The study of poly(dI-br5dC).poly(dI-br5dC) films by infrared spectroscopy shows that in low salt concentration, the conformation of this polynucleotide belongs to the B-family and in high salt concentration to the Z-family. 31P nuclear magnetic resonance and circular dichroism confirm the existence of these two forms. By circular dichroism and ultraviolet absorption, it is shown that the equilibrium constant of the B reversible Z transition depends upon temperature. The deuteration rates of exchangeable protons involved in hydrogen bonds between base pairs were deduced from the changes in absorbance near 1700 cm-1. In the B-form, one class of protons is measured with an exchange half-time of 20 minutes. In the Z-form, two classes of protons are measured with very different exchange half-times, the exchange half-time of the slow protons being of the order of 850 minutes. By comparison of these results with those previously obtained for poly(dG-dC).poly(dG-dC), these very slow protons of these two Z-polynucleotides are identified as the cytosine amino protons. A quantitative description of the dynamic structure of the Z-form is presented.

Circular Dichroism↗
PubMed1982

Comparison of poly(dG-dC).poly(dG-dC) conformations in oriented films and in solution.

The structures of B and Z forms of poly(dG-dC).poly(dG-dC) in oriented hydrated films have been investigated by infrared spectroscopy. First, the infrared linear dichroism spectrum of poly(dG-dC).poly(dG-dC) in B form (high relative humidity and 2 M Na+) was recorded. The spectrum of the Z form was recorded at a lower relative humidity and higher sodium content (4 M). The experimental conditions were similar to those used in x-ray diffraction studies of left-handed poly(dG-dC).poly(dG-dC) fibers. A qualitative agreement was found between the calculated values of the angles characteristic of the orientation of PO-2 groups with respect to the helical axis in the ZI form and the experimental values. The infrared spectra of B and Z form and the experimental values. The infrared spectra of B and Z forms show some significant differences in H2O and 2H2O. The deuteration rates of exchangeable protons involved in hydrogen bonds between guanine and cytosine residues were deduced from the changes in absorbance near 1700 cm-1. In the B form, the exchange half-time is of the order of 20 min. In the Z form, the exchange half-time of some protons is very slow, of the order of 24 hr. Because of the similarity between these values and those previously reported for the high-salt and low-salt form of poly(dG-dC).poly(dG-dC) in solution, we conclude that the high-salt form of poly(dG-dC).poly(dG-dC) in solution belongs to the Z family.

Kinetics↗
PubMed1980

Hydrogen exchange in hydrated films of proteins. Application to the E. coli lac repressor core.

An original easy method of hydrogen to deuterium exchange in hydrated films of proteins, followed by infrared absorption measurements, is described and applied to films of the E. coli lac repressor core, in order to examine the effect of isopropyl-beta-D-thiogalactoside (IPTG) binding. An estimation of about 25% alpha helical structure in this protein fragment is deduced from the exchange curve. The binding of IPTG to the core does not affect the exchange curve within the experimental error limits.

Deuterium↗
PubMed1975

Conformations and structural transitions in polydeoxynucleotides.

Polydeoxynucleotides of different base sequence, the alternating poly[d(A-T)]-poly[d(A-T)], crab satellite DNA, on the one hand, and double-stranded homopolymer complexes poly[d(A)]-poly[d(T)], poly[d(I)]-poly[d(C)], on the other, display significant differences in their conformation and conformational transitions. Infrared linear dichroism investigations indicate that the alternating poly[d(A-T)]-poly[d(A-T)], enzymatically synthesized, adopts a lower humidity a well-expressed A* form in which stability is relatively small,i.e., restricted to limited relative humidity. This A form is characterized by the orientation of the bisector of the phosphate OPO group at 34 degrees with respect to the helical axis, which is slightly lower than that of DNA. In contrast, for the homopolynucleotide double-stranded complex poly(dA)-poly(dT) and also for poly(dI)-poly(dC), the B yields A conformational change is not observed. Instead poly(dA)-poly(dT) exists at lower humidity in a stable modified B form. Thus the present results indicate that homo(dA)-homo(dT) double-stranded sequences prevent the B yields A structural transition. All AT-containing polydeoxynucleotides and crab satellite DNA adopt a high humidity a modified B form characterized by the orientation of the bisector of the phosphate group OPO at 64 degrees with respect to the helical axis which is significantly lower than 68-74 degrees observed in DNAs. The base pairing geometry in poly(dA)-poly(dT), poly[d(A-T)]-poly[d(A-T)], and also in poly(dI)-poly(dC) is apparently a Watson and Crick type. Thus the observed differences in conformation are not due to different base pairing scheme. It is suggested that in DNAs of high AT content the presence of homo(dT)-homo(dA) sequences and the relatively low stability of the A form of d(A-T) alternating sequences may inhibit the change to the A form. A possible role of these sequences in DNA recognition by protein is suggested.

Binding Sites↗
PubMed1973

Direct evidence of the C-like form of sodium deoxyribonucleate.

From infrared linear dichroism studies, direct evidence is given for a new Na DNA form, which is similar to the C form of Li DNA. This C-like form in Na DNA occurs under conditions of very low NaCl content (at high relative humidity), high NaCl content (at low relative humidity), and low G + C content of the DNA (at low relative humitiy). The C form of Li DNA was originally discovered by x-ray diffraction, but has not previously been characterized by infrared spectroscopy. The C form is primarily characterized by the orientation of the O2- -O3 line of the phosphate group, which is about 48 degrees (+/-2 degrees ) with respect to the helical DNA axis and which is different from that of the B and A forms. Na DNA molecules rich in A + T may entirely or partially adopt the C form at low relative humidity. Since from infrared evidence, the C-like form is found not only in Li DNA at low relative humidity but also in Na DNA under different conditions, the C form may be biologically important. A possible role for recognition by proteins is suggested.

Adenine Nucleotides↗