Distribution of isoaccepting tRNAs and codons for proline and glycine in collagenous and noncollagenous chicken tissues

The relation between codon usage and tRNA content for proline and glycine, the major constituents of collagen, was studied in two tissues: the magnum of laying hen oviduct and the leg tendons of chick embryo where collagen is produced. Although the relative contents of tRNA(GCCGly) and tRNA(IGGPro) in tendons, as compared to magnum indicate a specialization of the tRNA population for collagen synthesis, the distribution of the preponderant codons in collagen mRNA is correlated but at a lesser extent to that of their cognate tRNAs.     

Relative content of isoaccepting tRNAs for glycine and proline in avian tendon cells with different rates of procollagen synthesis

The relative amounts of iso-tRNAsGly and iso-tRNAsPro existing in chick embryo tendon are indicative of a specialization of the tRNA population for collagen synthesis. These amounts are not modified (i) in primary avian tendon (PAT) cells in culture for which the procollagen production varies from about 10% of total protein synthesis to 60% and (ii) in tendons from immature chicks, which show a 3-fold decrease of procollagen production with increasing age. The characteristic tRNA pattern was not maintained in cells which had lost the ability to make high levels of collagen as observed in the cases of: (i) PAT cells reaching confluency; (ii) virus-transformed PAT cells and (iii) tendon from adult chick. Our data are consistent with the idea that tendon tRNA specialization for collagen synthesis is a differentiation feature independent of the expression level of the collagenic function but related to its maintenance.     

Cerebral and ocular abnormalities with anterior pituitary insufficiency of familial nature

Three families presenting one or several cases of brain or ophthalmic abnormalities and an hypopituitarism at least by one of the members have been observed. In the first family, the mother and one of her sons present bilateral choroidoretineal coloboma with amblyopia; one of these two suffers as well from panhypopituitarism. In the second family two premature twins, a brother and his sister, present a syndrome with hypophyseal dwarfism and ophthalmic abnormalities, consisting in the boy's case in an peripapillary depigmentation with no visible sight trouble whereas girl's is showing an extreme microphthalmia with major mental retardation. In the third family two 2nd degree cousins present a panhypopituitarism but only one of the two reveals through neuroradiological investigations corpus callosum and septum lucidum agenesia. The karyotype is normal in all the cases. An hereditary mechanism appears clearly in the first family. It is possible in the second, probable in the third one.     

Fluorescence polarization of polypeptides having a fluorescent endgroup

The polarization of fluorescence of a chromophore chemically bound on the NH₂ end of a poly(L -benzyl glutamate) molecule has been studied as a function of temperature, viscosity, and solvent. The relaxation times depend on both the overall rotation of the helix and the local rotation of the endgroup. In m–cresol the endgroup is rigidly bound and the rotational diffusion constant of the molecule is in good agreement with the values obtained by Kerr effect and dielectric relaxation. In other helicogenic solvents (DMF, DCE, etc.) the local rotation is nearly free. In m-cresol-DMF mixtures a sharp decrease of the polarization around a composition of 40% DMF can be interpreted as a change in the freedom of rotation of the endgroup. No discontinuity in the optical rotation is observed in the solvent mixture. The question of how a rapidly rotating endgroup could show an extrinsic Cotton effect as observed by Bloutand Yamaoka for the system Acridine Orange–PBLG in chloroform is then raised. Polarization of fluorescence measurements on this system show a nearly complete freedom of rotation of the dye and OH D measurements show no detectable Cotton effect in the dye absorption band.     

Dynamics of single-stranded DNA in polyacrylamide gels during pulsed field gel electrophoresis. A birefringence study

The study of the orientation of single-stranded DNA in polyacrylamide gels in denaturing conditions has been undertaken by electric birefringence in order to determine the mechanism involved in the electrophoretic transport. The presence of an overshoot in the birefringence signal, when applying the electric field, and the study of the influences of the electric field and of the gel concentration on the dynamics show that a mechanism of reptation with elongation of the molecule occurs in polyacrylamide gels with low T values. Therefore it is suggested that the use of pulsed fields in sequencing electrophoresis is possible and can lead to a large increase of the length of the fragments that can be sequenced in one single run.     

Changements de l'epithélium médian des bourgeons palatins de souris au stade de préfusion

Résumé Avant d'entrer en contact, les surfaces de fusion des processus palatins subissent des modifications. Certaines cellules épithéliales superficielles deviennent turgescentes, alors que d'autres conservent un aspect dense et aplati, elles se lysent et éclatent. Des noyaux semblables à ceux des assises profondes se retrouvent en surface, paraissant migrer vers le bourgeon antagoniste. Des projections filamenteuses apparaissent, quelques unes établissant un contact avec l'épithélium opposé, d'autres restant seulement sous forme d'expansion. Ces observations sont concordantes en microscopie photonique et en microscopie électronique à balayage.

---

Modification of the medial epithelium of the palatal shelves of mice at the prefusion stage. A light and scanning electron microscopy study

Summary The fusion surfaces of the palatal processes are modified before coming into contact. Several superficial epithelial cells become hypertrophied, undergo lysis and burst, whereas others remain flattened and densely stained. Nuclei, similar to those localized in deeper layers are found on the surface and seem to migrate towards the opposite process. Filamentous projections appear and some establish a linkage with the opposite epithelium, whereas others expand freely from the surface. Light microscope observations agree with scanning electron microscopy findings.

     

Site binding as a local equilibrium. Mn2+ binding to poly(acrylic acid) as a function of the degree of ionization

Mn2+ binding to poly(acrylic acid) at different degrees of ionization, alpha, has been studied from the frequency dependence of the water protons' relaxation rates T1(-1) and T2(-1). Site binding is treated as an equilibrium with the concentration of free ions at the immediate vicinity (CIV) of the polyion. The CIV is calculated as the solution of the Poisson-Boltzmann equation at the surface of the cylindrical polyion. A single value of K is shown to fit the results at all values of alpha. The amount of site binding is higher than the total amount of condensed divalent counterions predicted for a finite polyion concentration in the presence of monovalent counterions by Manning's theory.     

Thymidylate synthetase catalyzed exchange of tritiumfrom [5-3H]-2'-deoxyuridylate for protons of water.

Thymidylate synthetase catalyzes an exchange of tritium of [5-3H]dUMP for protons of water in the absence of CH2-H4folate. The turnover number for this reaction is some 45,000-fold lower than that of dTMP formation and Km is 1.2 X 10(-5) M, similar to the dissociation constant of the enzyme-dUMP complex determined by equilibrium dialysis. The presence of 4 mM folate has no effect on Vmax but results in a decrease in the Km of dUMP to a value close to that in the normal enzymic reaction. The exchange reaction provides definitive evidence that the enzymic reaction involves attack of a nucleophile of the enzyme on the 6 position of dUMP to provide a 5,6-dihydro-dUMP intermediate which is covalently bound to the enzyme. Stereochemical considerations of the exchange reaction require proposal of a partial reaction which is not completely sterospecific or a complex reaction in which protons of water are handled with complete stereospecificity in a fashion similar to the one carbon unit of the normal enzymic reaction.