Comptes rendus de l'Academie des sciences. Serie III, Sciences de la vie最新文献

The lizard Lacerta vivipara is a seasonal breeder with a well characterized reproductive cycle. An histological study of the lizard testis has been performed at different stages of spermatogenesis and the nuclear basic proteins content was assessed by electrophoretical analysis. Two protamines, lacertines 1 and 2, are present in spermatozoa in April and May. We have isolated lacertine1 and characterized a protamine with a mass of 4,963.7 Da. Amino acid sequence of this protamine (41 residues) was established from data provided by automated Edman degradation. It is characterized by a basic amino acid stretch in the N- and C-terminal regions and by a central part which only consists of 3 different intermingled amino acids. This protamine presents 62% homology with scylliorhinine Z3 from dog-fish Scylliorhinus caniculus and 58% homology with quail protamine. The reported lizard protamine sequence is the first reptilian protamine sequence available so far.

We proposed previously a cyclic code made of 22 triplets, which we now call the AB code. It is made up of the following chain: AUGGUGCCAUUCAAGACUAUGA. The letters A, U, C, G represent the classical symbols of the (purine and pyrimidine) bases of the genetic code. This chain presents the following features: (1) when it is in cyclic form, it begins with the initiation codon AUG, ends with the termination codon UGA, and it can be read triplet after triplet by choosing 1 and only 1 representative of each synonymy class in the classical degenerate genetic code made of 64 triplets. The chain, therefore, possesses 1 and only 1 codon for each amino-acid; (2) except for the doublet CG, triplets of the chain begin with the 15 other possible doublets of bases (satisfying the "wobble" hypothesis presented by Crick); (3) it corresponds (except for 1 base) to the "loop" part of the CEnothera mitochondrial Gly-tRNA; (4) it can be modified, without loss of the properties (1) and (2), in such a way as to have 15 bases in common with the loop part of other mitochondrial tRNA's considered as primitive, like Ala-, Pro- and Arg-tRNA; (5) it contains the most frequent triplets, but not the most rare ones, appearing in the genome of numerous species; (6) it exhibits a coherent internal structure with respect to the molecular weight of its triplets. This structure, also found in the loop part of mitochondrial tRNA's, contains an excess of AU bases with respect to GC bases. This fact has no explanation in the classical probabilistic model of the tRNA's. Therefore, we propose the cyclic AB code as a primitive genetic structure with the essential coding properties of the present genetic code.

About half of the mitochondrial DNA of the shrimp Penaeus notialis (Crustacea: Decapoda) has been cloned (in 2 overlapping fragments of 7.9 kb and 1 kb) and partially sequenced. The gene content and arrangement are identical to that of the homologous domain in Drosophila yakuba. Intergenic nucleotides are scarce and a 982 bp non-coding sequence exhibit features similar to that of mtDNA control regions. The gene organization and the tRNA structures differentiate the Penaeus notialis mitochondrial genome from that of Artemia franciscana. Paraphyletism of crustacean mtDNA with respect to Insecta is discussed. A secondary structure of s-rRNA is proposed.

The in vitro activation of murine macrophages by horseradish peroxidase (HRP) induced nitric oxide production in a dose-dependent manner, and increased the induction of NO-synthase by LPS. Nitrite production after HRP stimulation was inhibited by NG-monomethyl-L-arginine (NMMA), a specific inhibitor of NO-synthase. Equivalent amounts of nitrite were obtained with native and heat-inactivated HRP. High concentrations of mannose inhibited nitric oxide production, while the HRP inhibitor 3-aminotyrosine did not. Glycosylated serum albumin derivatives also induced murine macrophage NOS, probably by an interaction between carbohydrates and their specific cell membrane receptors. The inability of HRP apoprotein to stimulate NO production, and the specific inhibition of HRP-mediated activation of macrophages by hemin suggests that the heme moiety of this enzyme is involved in NO-synthase induction.

Electron microscopy of DNA, either free or complexed with ligands, allows the analysis of local conformational variations along individual molecules. Electron microscopy is unique, in that it has the capacity to determine the average behaviour of a population of molecules observed individually, and can thus provide a better appreciation of variability within the series of molecules than biophysical or biochemical methods. Very encouraging results have been obtained by cryoelectron and near-field microscopies, especially atomic force microscopy, in parallel with traditional techniques for visualizing DNA molecules adsorbed onto a support film. Differences in sample processing procedures and image formation modes render these 3 types of microscopies complementary. The torsional stress of a DNA molecule together with a local curvature induced by the protein MC1 from archaebacteria, can be detected within minicircles comprising 207 base pairs.

We have previously isolated 3 different populations of clathrin coated vesicles (CCV) involved in the LDL-receptor traffic in bovine adrenal cortex. We now show that each CCV type contains the transferrin-R and the CI-MPR, therefore, they provide a good model for studying the membrane organization that may govern their targeting in one of the biosynthetic, endocytic and/or recycling pathways. Transferrin--prototype of recylcing ligand--, and alpha adaptin, dynamin and the 110 kDa phosphatidylinositol-3-kinase subunit--of the trafficking machinery--were mainly detected in only 2 of the vesicle populations which could be involved in the endocytic/recycling pathway. The third population which contained larger amounts of gamma adaptin and do not carry transferrin could be involved in the biosynthetic pathway. The vesicle lipid pattern and the saturation of their fatty acyl chains were analyzed and confirmed these results. The nature of the interactions between vesicle components was then determined using several classes of detergents. Only non ionic ones could solubilize the LDL-R in a complex with either alpha or gamma adaptin. In contrast, they dissociated clathrin or beta-beta' adaptins. Taken together these results prompt us to suggest an integrated model for targeting in membrane traffic. Besides specific targeting signals carried by cargo proteins and recognized by proteins from the coat and the cytosolic trafficking machinery, lipids would play a key modulatory role. At each step in the membrane traffic, the proteins which carry multiple targeting signals would interact transiently with a specific set of lipids. This would result in the exposure of the appropriate targeting signals which could now become recognized by the proper targeting machinery.

A linear electron accelerator, operated in a recurrent chopped mode, was used for time-resolved investigation of split-dose radiation recovery in 3 mammalian cell lines in vitro. The time intervals separating the sequential radiation exposures in this study ranged from fractions of a second to a few minutes. The primary pulse brought about rapid, synchronous oscillations of cellular radiosensitivity giving rise to a tetraphasic, W-shaped time-dependent profile whose first phase was accomplished by a large decrease of cell survival. Only the last phase correlated with sub-lethal damage repair determined by gamma-ray irradiation. The same profile was observed for the 3 cell lines investigated. However, the kinetics of the whole process varied extensively from one cell line to another. The first phase lasted 1 s only for Chinese hamster V79 fibroblasts, 6 s for human squamous carcinoma SQ20B cells, and as much as 25 s for human colon adenocarcinoma LoVo cells. The relative amplitude of this first phase grew with both the first and second radiation doses in the range explored. It is hypothesized that rapid oscillation of the cytotoxic potential of radiation may result from various mechanisms such as molecular recognition of radio-induced lesions, changes in chromatin structure, or differential activation of phospholipid-dependent transduction pathways.

The yeast Sup35p protein which is responsible for the [psi] phenotype, is a GTP-binding protein involved in translation termination. It was suggested recently that the [psi] determinant has prion-like properties that were localized in the 114 N-terminal amino acids of the protein. In this study, we show that the 5' end of the human SUP35 gene open reading frame is longer than previously reported by 138 codons. This N-terminal sequence presents similarities with the N-terminus of S. cerevisiae Sup35p protein, involved in [psi] maintenance. By transfection of human cells and Western blotting, we demonstrate that translation is initiated at the first AUG encountered at the 5' end of the human SUP35 gene. The longest form of the protein, which contains the N-terminal extension, is the major form of Sup35p protein in non transfected cells. Moreover, an analog of the long form of Sup35p protein is found in various mouse tissues. We suggest that the protein encoded by SUP35 gene could have, at least in human, the properties described for the yeast [psi] element.

A well preserved mouse skull has been recovered from a pedogenically modified mudstone layer (c. 2 millions years (MY) old) of Pinjor Formation (Upper Siwaliks) exposed east of Chandigarh, India. Comparison of the present skull with those of the extant species of the subgenus Mus reveals its closer relationship towards the house mouse Mus musculus lineage. The present fossil evidence is very much in line with the molecular, allozymic and ecological proposals for the time and place of origin of the subgenus Mus.

We have devised a model in which nude mice are T cell reconstituted at birth by subcutaneous grafts of embryonic thymic epithelium (TE) removed from 10 days allogeneic embryos. The TE is colonized by the nude mouse hemopoietic cells which differentiate into T cells. Such T cell-reconstituted nude mice are able to reject third party skin graft and are tolerant to skin of their own haplotype but also the TE H-2 type. We have recently shown that this tolerance can be transferred by CD4+ peripheral T cells selected on the allogeneic TE. The question as to whether such T cells can regulate the activity of effector cells from normal mice is addressed here. We show that the transfer of peripheral T cells issued from such chimeras, together with syngeneic T cells from normal mice, into nude recipients induces a significant delay in the rejection of skin graft of the TE haplotype. This delay depends on the ratio of the 2 types of injected cells. This demonstrates that regulatory T cells selected on an allogeneic TE are able to control the effector activity of peripheral T cells issued from normal mice. The T cells selected on the allogeneic TE can therefore be considered as endowed with a negative regulatory activity with respect to the process leading to effector cells activation.