Somatic hyperconversion diversifies the single Vh gene of the chicken with a high incidence in the D region

The chicken heavy chain locus contains a single JH segment and a unique functional VH gene (VH1) 15 kb upstream, with approximately 15 D elements in between. A cluster of pseudogenes (psi VH) spans 60-80 kb, starting 7 kb upstream from VH1, with an average density of one pseudogene per 0.85 kb and an almost systematic alternation of polarity. Diversification of the unique rearranged VH1 gene takes place during bursal ontogeny by the same hyperconversion mechanism that was described for the chicken light chain, with psi VH segments acting as donors. The hyperconversion mechanism also operates within the D region, as all pseudogenes analyzed are fused VD elements; this D region possesses distinct characteristics, allowing higher combinatorial possibilities in the gene conversion process. Allelic exclusion appears to be performed by restriction of a complete VDJ rearrangement to a single allele.     

Light chain gene conversion continues at high rate in an ALV-induced cell line.

We have analyzed immunoglobulin light chain sequences from avian leukosis virus (ALV) induced bursal and metastatic tumors and from cell lines derived from these tumors. Sequence data presented demonstrate that ALV-induced tumors and one cell line (DT40) derived therefrom continue to diversify their light chain genes outside of the bursal environment. Diversification within these tumor cells seems to occur by gene conversion events comparable with those observed in bursal B cells. Sequence analysis of spontaneously arising surface immunoglobulin negative subclones of the DT40 cell line revealed frameshifts within the rearranged light chain genes which most likely resulted from non-functional recombination events. Superimposed gene conversion events can repair these frameshifts leading to re-expression of surface immunoglobulin.     

Sensitized fluorescence in polynucleotide-dye complexes and the problem of energy transfer in polynucleotides

New results on sensitization of fluorescence of Profiuvine, Acridine Orange and Ethidium Bromide complexes wilh double stranded poly A-poly U upon ultraviolet irradiation are presented. Together with older results on dye DNA complex, they are interpreted to show that base to base transfer plays essentially no role compared to direct base to dye transfer. A lower limit of base to base transfer time (which is at the same time a higher limit for life time of fluorescence) in DNA (2. 10^?11 sec.) and poly A-poly U (2. 10^?13 sec.) is obtained which cast some doubt upon the validity of calculations of optical properties using the exciton (strong coupling) approximation.     

Polarization of fluorescence of an oriented solution of rodlike particles bearing a fluorescent label

The variation of the polarized components of fluorescence of a rodlike particle bearing a fluorescent label upon partial orientation is calculated for some special geometry of the dye macromolecules complexes. Explicit expressions are given for the case where the energy of the molecule in the field depends only on one angle θ, showing that the result is a function of both 〈sin²θ〉 and 〈sin⁴θ〉. For the case of orientation in an electric field through an anisotropic induced moment, the expressions allow the calculation of this anisotropy of polarizability. The method is applied to the measurement of the polarizability of rodlike fragments of DNA labeled by intercalated molecules of Acridine Orange.     

NMR and density study of Co site binding by polyelectrolytes

The changes of density and chemical shifts of the water proton upon addition of CoCl₂ to aqueous solutions of tetramethylammonium salts of seven polyelectrolytes (polyphosphate, maleic acid-methylvinylether alternated copolymer, polyacrylic acid, carboxymethylcellulose of substitution degree 0.98, 1.3, 2.1, 2.65) have been measured. Assuming a negligible contribution of pseudo-contact interaction to the water proton chemical shift and a constant hyperfine constant upon displacement of water molecules by other ligands, has permitted the calculation of (i) the number of water molecules released by Co²⁺ ions upon binding and the approximate fraction of Co²⁺ ions bound with loss of water, and (ii) the total volume change upon binding and the individual contributions of counterions and polyelectrolyte charged sites to this volume change. Our results are generally in agreement with those obtained using other methods.     

Orientation and stretching of DNA chains during pulsed field gel electrophoresis

The quantitative analysis of the decay of birefringence accompanying gel electrophoresis leads to the characterization of two phenomena respectively attributed to alignment of the tube and to overstretching of the chain in its tube. The major contribution to the molecular orientation is given by the overstretching which relaxes according to a stretched exponential law. The other process, slow, is characterized by a reptation time and a mean orientation factor in good agreement with the biased reptation model without overstretching.     

Linkage of plasminogen (PLG) and apolipoprotein(a) (LPA) in baboons.

Four allelic forms of serum plasminogen (PLG) were detected in baboons (Papio hamadryas Linneaus 1758) by isoelectric focusing and were determined to be inherited as autosomal codominant traits. Linkage analysis of data from 179 progeny and their parents revealed that PLG is tightly linked (lod score = 30.20) to the gene encoding apolipoprotein(a) (LPA), as in humans. No recombinant individuals were identified. This is the first linkage detected between PLG and LPA in any species other than humans and is the first genetic linkage identified in a nonhuman primate species by family studies.