Roles moleculaires des proteines de choc thermique dans le fonctionnement des organismes a des temperatures normales et suite a des chocs thermiques; differents genes impliques

The heat-shock proteins

In the genome of a germ-line cell, the genetic information for an immunoglobulin polypeptide chain is contained in multiple gene segments scattered along a chromosome. During the development of bone marrow-derived lymphocytes, these gene segments are assembled by recombination which leads to the formation of a complete gene. In addition, mutations are somatically introduced at a high rate into the amino-terminal region. Both somatic recombination and mutation contribute greatly to an increase in the diversity of antibody synthesized by a single organism.

Somatic generation of antibody diversity

I read this book the same weekend that the Packers took on the Rams, and the experience of the latter event, obviously, colored my judgment. Although I abhor anything that smacks of being a handbook (like, \"How to Earn a Merit Badge in Neurosurgery\") because too many volumes in biomedical science already evince a boyscout-like approach, I must confess that parts of this volume are fast, scholarly, and significant, with certain reservations. I like parts of this well-illustrated book because Dr. Sj6strand, without so stating, develops certain subjects on technique in relation to the acquisition of judgment and sophistication. And this is important! So, given that the author (like all of us) is somewhat deficient in some areas, and biased in others, the book is still valuable if the uninitiated reader swallows it in a general fashion, realizing full well that what will be required from the reader is a modulation to fit his vision, propreception, adaptation and response, and the kind of problem he is undertaking. A major deficiency of this book is revealed by comparison of its use of physics and of chemistry to provide understanding and background for the application of high resolution electron microscopy to problems in biology. Since the volume is keyed to high resolution electron microscopy, which is a sophisticated form of structural analysis, but really morphology in a modern guise, the physical and mechanical background of The instrument and its ancillary tools are simply and well presented. The potential use of chemical or cytochemical information as it relates to biological fine structure , however, is quite deficient. I wonder when even sophisticated morphol-ogists will consider fixation a reaction and not a technique; only then will the fundamentals become self-evident and predictable and this sine qua flon will become less mystical. Staining reactions (the most inadequate chapter) ought to be something more than a technique to selectively enhance contrast of morphological elements; it ought to give the structural addresses of some of the chemical residents of cell components. Is it pertinent that auto-radiography gets singled out for more complete coverage than other significant aspects of cytochemistry by a high resolution microscopist, when it has a built-in minimal error of 1,000 A in standard practice? I don't mean to blind-side (in strict football terminology) Dr. Sj6strand's efforts for what is \"routinely used in our laboratory\"; what is done is usually well done. It's just that …

Methods in Enzymology.

The events of the cell cycle of most organisms are ordered into dependent pathways in which the initiation of late events is dependent on the completion of early events. In eukaryotes, for example, mitosis is dependent on the completion of DNA synthesis. Some dependencies can be relieved by mutation (mitosis may then occur before completion of DNA synthesis), suggesting that the dependency is due to a control mechanism and not an intrinsic feature of the events themselves. Control mechanisms enforcing dependency in the cell cycle are here called checkpoints. Elimination of checkpoints may result in cell death, infidelity in the distribution of chromosomes or other organelles, or increased susceptibility to environmental perturbations such as DNA damaging agents. It appears that some checkpoints are eliminated during the early embryonic development of some organisms; this fact may pose special problems for the fidelity of embryonic cell division.

https://science.sciencemag.org/content/sci/246/4930/629.full.pdf

Checkpoints: controls that ensure the order of cell cycle events

A bacterial cloning system for mapping and analysis of complex genomes has been developed. The BAC system (for bacterial artificial chromosome) is based on Escherichia coli and its single-copy plasmid F factor. It is capable of maintaining human genomic DNA fragments of greater than 300 kilobase pairs. Individual clones of human DNA appear to be maintained with a high degree of structural stability in the host, even after 100 generations of serial growth. Because of high cloning efficiency, easy manipulation of the cloned DNA, and stable maintenance of inserted DNA, the BAC system may facilitate construction of DNA libraries of complex genomes with fuller representation and subsequent rapid analysis of complex genomic structure.

/pdf/cloning-and-stable-maintenance-of-300-kilobase-pair-rv1nam7ysh.pdf

Cloning and stable maintenance of 300-kilobase-pair fragments of human DNA in Escherichia coli using an F-factor-based vector.

Structural Transitions During Maturation of Bacteriophage Lambda Capsids

https://mmbr.asm.org/content/mmbr/42/3/529.full.pdf

Head morphogenesis of complex double-stranded deoxyribonucleic acid bacteriophages.

The morphogenesis of bacteriophage lambda. IV. Identification of gene products and control of the expression of the morphogenetic information.

The kappa light chain genes from two mutant hybridoma cell lines defective in kappa light chain synthesis were isolated and compared to the wild-type kappa light chain gene. In each case, the mutant kappa light chain genes were found to contain repetitive DNA elements in their intervening sequences that were not present in the intervening sequences of the wild-type kappa light chain gene. These elements were found to be related to the genes of intracisternal A particles. These results suggest that the decreased production of kappa light chain in the mutant cell lines is due to the presence of the intracisternal A particle-related genes.

https://www.pnas.org/content/pnas/79/23/7425.full.pdf

Mutant immunoglobulin genes have repetitive DNA elements inserted into their intervening sequences

The mature chromosome of bacteriophage X is a linear duplex of a unique sequence 48,502 nucleotide pairs long (34). The 5'-terminal ends of this molecule protrude as self-complementary single-stranded chains of 12 nucleotides which can anneal to generate circles. When a X DNA molecule is injected into the host, it is circularized and closed covalently by DNA ligase action. Early during lytic infection, X DNA undergoes several rounds of replication in which circles generate circles. At later times of infection, rolling-circle replication takes over and individual rings give rise to linear concatemers (3, 8, 9, 28) which may be 10 chromosomal units long (in the absence of packaging). During DNA packaging, monomeric chromosomal units are cut from these replicative oligomers by the enzyme X DNA terminase, which regenerates the unique single-stranded ends by introducing two specific nicks staggered 12 nucleotides apart on opposite strands of the duplex, followed by melting of the joint. The DNA site of action of terminase is called cos. By its interaction with cos, terminase not only catalyzes the formation of ends but, in coupling proheads to DNA, establishes the origin and direction of packaging. The overview model for packaging and cutting of X DNA which is currently accepted is as follows: (i) random selection of a cos site from among those present on a concatemer for packaging initiation, (ii) polarity of chromosome entry into the prohead from the Nul end to the R end, (iii) dependence of cos cutting on the packaging of a minimal length ofDNA, and (iv) processive packaging oftwo or three chromosomes in series from a concatemer (8, 9, 28). For previous reviews on this subject, see references 8, 9, and 28. With a few exceptions, references included in these reviews will not be cited specifically; instead, the reader will be directed to one or more of these three reviews, as the case may be.

Helios Murialdo

Papers

Structural Transitions During Maturation of Bacteriophage Lambda Capsids

Head morphogenesis of complex double-stranded deoxyribonucleic acid bacteriophages.

The morphogenesis of bacteriophage lambda. IV. Identification of gene products and control of the expression of the morphogenetic information.

Mutant immunoglobulin genes have repetitive DNA elements inserted into their intervening sequences

Bacteriophage lambda DNA: the beginning of the end.