Showing papers on "Regulation of gene expression published in 1975"

The appearance of new structures and functions in proteins during evolution.

Abstract: The likelihood of a de novo generation of classes of efficient proteins through neoformation of DNA, through modification of expressed DNA, and through modification of nonexpressed DNA is examined. So is the likelihood that newly formed inefficient enzymes be turned into efficient enzymes. The conclusions are that neither gene duplicates nor dormant genes represent promising materials for a de novo generation of protein classes, that (with exceptions) such generation is unlikely to have taken place in recent evolution, that new structural genes must nearly consistently derive from preexisting structural genes, and that new functions can be evolved only on the basis of old proteins. Conditions of protein evolution in prokaryotes suggest that the saltatory formation of protein classes is as unlikely in prokaryotes as in eukaryotes. Data on the history of a few protein classes are reviewed to illustrate the preceding inferences. The analysis leads to the hypothesis that most protein classes originated before the major elements of the translation apparatus of modern cells were fully evolved. If simple sequence DNA is turned into structural genes by evolution, this process (again with exceptions) is considered to have taken place only at that very remote period. A polyphyletic origin of proteins is thought to date back to the same era. It is proposed that the development of genic multiplicity and of marked structural and functional diversity of proteins may have come about in the earliest cells primarily through the independent generation of structurally different polymerases in different protocells, followed by cell conjugation and the subsequent use by enriched cells of supernumerary types of polymerase for evolving further functions. Functional growth, as it took place at early times, is briefly discussed as well as functional change. The foundations for new functional developments in old proteins are analyzed. In considering the evolutionary recovery of lost functions, aspects of cell differentiation and gene regulation are linked with the evolutionary picture. The distinction between eurygenic and stenogenic control of gene activity is used. Next to gene deletion, cell and tissue deletion is held to be an event of general evolutionary significance, through cell and tissue origination that presumably accompanies the restoration of a lost molecular function.

Gene expression and macromolecular synthesis during preimplantation embryonic development.

Abstract: The most extensively studied systems of early embryonic development are ones far removed from man and other mammals and include, most notably, the echinoderms and amphibia. Based on work with these and other organisms, there has been built-up an overall picture in which much, if not all, of early post-fertilization development is controlled by messenger RNAs (mRNAs) which are synthesized in the egg but are not activated until after fertilization has occurred (Gross, 1967; Davidson, 1968; Brown and Dawid, 1969; Brachet and Malpoix, 1971). The presence and activity of such masked messenger RNAs (mmRNAs) were originally defined in experiments in which early development was shown to be invulnerable to the effects of actinomycin D, an inhibitor of RNA synthesis. However, the physical existence of these mmRNAs now seems to be firmly established, and it has been possible to isolate and use them to govern protein synthesis in vitro (Gross, et al. 1973; Skoultchi and Gross, 1973). With the development of techniques for the biochemical analysis of the mammalian embryo, it is natural that the question of how early mammalian development is controlled should be of great interest. While the presence or absence of mammalian mmRNAs has not as yet been established, the available information indicates that all stages of preimplantation mammalian development are affected by the genetic activity of the embryo itself. It will be the purpose of this paper to summarize the relevant information obtained principally from our own studies on the preimplantation mouse embryo and, when applicable, from the studies of others with mouse and rabbit embryos. Unless otherwise stated, the material will refer to the developing mouse embryo. between fertilization and implantation. Recent reviews of this subject have been published by Wolf and Engel (1972), Fowler and Edwards (1973), and Biggers and Stern (1973). The evidence will be reviewed in order from the least to the most direct, and the major point to be considered will be the role of embryonic gene action in governing early mammalian development. However, although our emphasis is on genetic control, it is well to keep in mind that gene activity by itself is unlikely to be the whole explanation of development and differentiation. This point was well stated in a recent book by Wright (1973). “Application of the words cause’ or trigger’ to particular components within a differentiating system may delude the user into feeling that there exist certain ‘spontaneous’ or independent factors uniquely capable of causing differentiation to occur. . . . There is no a priori reason for singling out any particular biochemical event on which differentiation depends as being more essential or necessary than others. ... Such an approach renders an objective analysis difficult and stresses the role of components which may or may not be limiting the rate of the differentiation process in question. It appears to be no more justilied or useful to choose selective gene activation as ‘the’ basis of differentiation than to choose, for example, substrate availability.”

Histidine regulation in Salmonella typhimurium: an activator attenuator model of gene regulation.

Abstract: An activator-attenuator model of positive control, a s opposed to the classic repressor-operator model of negative control, is proposed for the major operon-specific mechanism governing expression of the histidine gene cluster of Salmonella typhimurium. Evidence for this mechanism is derived from experiments performed with a coupled in vitro transcription-translation system, as well as with a minimal in vitro transcription system [Kasai, T. (1974) Nature 249, 523--527]. The product (G enzyme, or N-1-[5'-phosphoribosyl]adenosine triphosphate:pyrophosphate phosphoribosyltransferase; EC 2.4.2.17) of the first structural gene (hisG) of the histidine operon is not involved in the positive control mechanism. However, a possible role for G enzyme as an accessory negative control element interacting at the attenuator can be accommodated in our model. The operon-specific mechanism works in conjunction with an independent mechanism involving guanosine 5'-diphosphate 3'-diphosphate (ppGpp) which appears to be a positive effector involved in regulating amino-acid-producing systems, in general [Stephens, J.C., Artz, S.W. & Ames, B.N. (1975) Proc. Nat. Acad. Sci. USA, in press].

A cis -dominant regulatory mutation affecting enzyme induction in the enkaryote Aspergillus nidulans

Abstract: STUDIES on cis-acting regulatory mutants (for example, operator and promoter mutants) in bacteria have been of crucial importance in understanding gene regulation1–4 Similar mutants in eukaryote systems have not been extensively studied although there have been two reports of probable operator constitutive mutants in yeast5,6 An understanding of eukaryote genetic organisation and gene regulation requires that mutants affecting the regulation of adjacent genes of defined function be isolated and characterised This communication describes a mutant of Aspergillus nidulans that is altered in a site closely linked to the structural gene (amdS) for acetamidase (EC3514)7,8 and results in increased inducibility of this enzyme by acetamide It is further shown that this mutation is cis-dominant in its effects

Chromosome-21-dosage effect on inducibility of anti-viral gene(s).

Abstract: UNLIKE the bacterial situation little is known about gene regulation in mammalian cells. Inducible systems are being used to study regulatory gene functions in normal and abnormal mammalian cells1–3, and have shown for example, that inhibitors of macromolecular synthesis enhance rather than inhibit the expression of an inducible enzyme. Actinomycin D enhances the induction of tyrosine aminotransferase (TAT) by steroid hormones in hepatoma cells4. Commonly referred to as superinduction, this effect has led to the hypothesis that a regulatory gene(s) modulates the expression of the structural TAT gene4. Of course, alternative explanations have been offered for the superinducing effect of actinomycin D (refs 5 and 6). Similarly, the induction of interferon by viruses and poly(I)·poly(C) and the induction of the anti-viral state (AVS) by interferon have been used to probe regulatory mechanisms in normal mammalian cells7–13. It has been demonstrated that with judicious use of metabolic inhibitors the amount of interferon and the level of AVS induced can be enhanced 100–1,000 times and 10–100 times respectively, over that obtained in cultures exposed to inducer alone. This suggested that one or more regulatory gene(s) modulate the expression of the structural gene for interferon and AVS7–19 I have used a new approach to assess the presence of a regulatory gene function which modulates the expression of the structural gene for AYS. 1 found evidence to suggest that the regulation of ithe anti-viral genes in human cells is controlled by regulatory gene element(s) located on a separate chromosome.

Genetic evidence on the organization and action of the qa-1 gene product: a protein regulating the induction of three enzymes in quinate catabolism in Neurospora crassa.

Abstract: The first three reactions in the catabolism of qainic acid in Neurospora crassa are under the genetic control of the qa gene cluster. This cluster consists of three structural genes encoding three inducible enzymes plus a regulatory gene (qa-1+) whose diffusible product apparently acts in a positive fashion to initiate coordinate synthesis of the three enzymes when an appropriate inducer is present. Genetic and biochemical evidence for both complementing and temperature-sensitive qa-1 alleles indicates that the product of the qa-1+ gene is an oligomeric (multimeric) protein. On the basis of cis-trans tests of appropriate double mutants (plus genetic mapping data for temperature-sensitive mutants), at least certain constitutive mutants (which produce all three qa enzymes in the absence of an inducer) are mutants in the regulatory gene and not in controlling elements such as initiators. The detection of stable (non-revertible) qa-1 intralocus deletion (multisite)mutants provides additional evidence for positive regulation in the qa system. Extensive genetic recombination data provide evidence that the two types of qa-1 mutants--slow-complementing (qa-1-s) and fast-complementing (qa-1-f)--map in discrete, non-overlapping segments of the qa-1 locus. These two distinct types of mutants are hypothesized to produce altered regulatory protein molecules that fail to interact either with a DNA initiator site (qa-1-s types) or with an inducer (qa-1-f types). The striking similarities between the qa system in this lower eukaryote and certain prokaryote operon systems are discussed.

Mutagenesis and genetic analysis with Chinese hamster auxotrophic cell markers.

Abstract: Chinese hamster ovary cells were treated with various physical and chemical mutagens and subject to the bromodeoxyuridine plus visible light procedure for isolation of auxotrophic mutants. more than 200 auxotrophs have been isolated which require exogenous supplement of various nutrilites for growth, such as glycine, adenine, thymidine, inositol, etc. Fifty-five of these have been characterized by complementation tests and were shown to constitute 15 different loci. All these auxotrophs are highly stable and exhibit all-or-none growth response to the respective nutrilites. Enzyme deficiencies have been identified in several of these classes. When these auxotrophs are hybridized with human cells and grown in selective medium, the hybrids lose human chromosomes at a rapid rate and the analysis for synteny of the human genes can be successfully carried out. Moverover, in hybrids formed between an adenine-requiring auxotroph and human cells, a human esterase activator gene has been identified which appears to regulate the expression of esterase gene activities in the Chinese hamster genome. Studies of this kind may lead to the understanding of gene regulation in mammalian cells.

Developmental biology : pattern formation, gene regulation

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The proteins of polytene chromosomes of Drosophila hydei.

Abstract: It is reported that chromatin can be prepared from highly purified polytene nuclei from the salivary glands of third instar larvae of Drosophila hydei; such chromatin differs from that of diploid nuclei mainly by deficiencies in certain nonhistone chromosomal proteins. It is suggested that these proteins are important components of constitutive heterochromatin, which is severely underrepresented in polytene chromosomes. Chromosome morphology, including the pattern of induced puffs, is maintained throughout the mass isolation of glands and sucrose gradient purification of nuclei, as indicated by studies on temperature-shocked and control larvae. No significant alteration in the chromosomal proteins following puff induction by heat shock could be detected on analysis of the isolated protein fractions by disc gel electrophoresis. More sensitive techniques must be developed to study the apparent rearrangement or accumulation of protein at puff sites, and to elucidate the role of this protein in gene activation.

Regulation of gene expression in Salmonella phage P22. II. Regulation of expression of late functions.

Abstract: Transactivation experiments were performed involving the genetically related Salmonella phages P22, L and Px 1 in order to find out if more than one positively acting regulatory product is engaged in the expression of vegetative gene functions of each of these phages. The results obtained with Px 1 - and L-lysogenic cells superinfected with P22 suggest the following conclusions: 1. The expression of the early genes 12 and 23 and of the late gene 19 (lysozyme synthesis) is positively regulated by two different regulatory products, since P22 transactivates in prophage Px 1 both early and late genes (Prell, 1973), in prophage L only late genes. 2. The transactivation by P22 of the lysozyme gene of prophage L takes place in the presence of L repressor. This conclusion is suggested, since the superinfecting P22 does not derepress early gene expression (see 1.), and is confirmed by demonstration of replication inhibition for L phage in L lysogenic cells doubly superinfected with L and P22 phages (Thomas-Bertani-experiment). 3. The late gene regulatory protein seems to be synthesized by gene 23, as transactivation experimetns with both L- and Px 1 , prophages suggest. 4. The expression of gene 23 itself is turned on by an early regulatory product. The gene which codes for it is still unidentified. However its product seems to by highly specific, since it is active on Px 1 - but not on L-prophage.

Regulation of expression of lac operon by a novel function essential for cell growth

Abstract: THE study of the in vitro transcription of the lac operon using a soluble fraction of bacteria and DNA containing the genes of the lac operon, indicates that gene expression is controlled by both the inducer–operator interaction1 and the action of cyclic AMP2–6. We have studied the mutant tsC42 (described previously7) and report that the in vivo expression of the lac operon is under the control of a phase-specific protein which is only synthesised or activated 20–30 min before cell division. This protein is essential for both the formation of membrane components and cell growth, as described previously7. We describe procedures for the isolation of the mutant and report its specific inability to express the lac operon at the transcriptional level.

Biochemistry of the cell nucleus : mechanism and regulation of gene expression

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Isolation of regulatory mutants in Saccharomyces cerevisiae.

Abstract: Publisher Summary This chapter describes isolation of regulatory mutants in Saccharonyces cerevisiae. Regulatory mutations have been invaluable in the study of genetic control in Escherichia coli. Operator and repressor mutations have defined these regulatory genes and given insights into the physiology of regulation. By studying double mutants and dominance in heterozygotes, it is possible to obtain a picture of the regulatory circuit and regulatory interactions. A difficult technical problem exists in the isolation of mutations that affect controlling elements or regulatory genes in most systems. Regulatory mutations do not usually alter the growth characteristics of the wild type, and therefore have no distinguishing phenotype. To identify regulatory mutants, one has to devise conditions under which regulatory mutations have a clear-cut phenotype. The chapter reviews studies on gene regulation in yeast to identify those techniques that have been most successful in selecting regulatory mutants. Arginine biosynthesis and arginine degradation is discussed and controls linking arginine catabolic and anabolic enzymes are explained in the chapter. The chapter describes acid phosphatase biosynthesis, pyrimidine biosynthesis, methionine biosynthesis, and histidine biosynthesis.

Gene activation during spermatogenesis

Abstract: Cell differentiation during spermatogenesis in the rat has been analyzed in terms of the formation of specific "marker" enzymes. Hyaluronidase and other acrosomal enzymes are formed in spermatids according to a highly predictable time schedule which may be termed a "molecular biological clock". The acrosomal enzymes beta-galactosidase and N-acetyl-beta-glucosaminidase exist as isoenzyme forms distinct from enzymes with similar substrate specificities in the lysosomes of precursor cells. Differentiation of spermatids thus involves the loss of gene expression for lysosomal enzymes and the activation of genes for acrosomal isoenzymes. Spermatogenesis is characterized by the sequential loss of expression of many genes, as evidenced by the loss of beta-glucuronidase in the differentiation of spermatogonia to spermatocytes, and the loss of uridine diphosphatase activity in the differentiation of spermatocytes to spermatids. The apparent absence of ornithine decarboxylase activity from spermatids suggests a dependence of these cells upon Sertoli cells for the provision of putrescine and/or spermidine. Such biochemical cooperativity among germinal cells may be necessary as the genes of spermatids are repressed and late spermatids become metabolically inactive. Spermatogenesis is also characterized by changes in the cellular content and rates of synthesis and phosphorylation of specific acidic chromatin proteins. It is hypothesized that these proteins may participate in the activation or repression of genes during spermatogenesis.

The nucleated erythrocyte: a model of cell differentiation.

Abstract: The process of erythropoiesis is characterized by several distinctive features which render it a very useful model of cell differentiation. Mature erythrocytes arise from stem cells in a series of intermediate stages which are fairly well defined both on morphological and on biochemical grounds. During this development, the erythrocytes genome is gradually inactivated and the cell becomes geared to the production of primarily one gene product, hemoglobin. Recently, erythropoiesis has been closely studied in avian species since it has become technically possible to fractionate the blood of anemic birds into high-yield populations of young, developing and mature red cells. Attention has focused on patterns of RNA synthesis including globin m-RNA, in relation to cytoplasmic constitutents becoming modified for reduced activity. From the point of view of gene regulation, erythrocyte development is especially interesting in non-mammals, where in contrast to mammals, even fully mature red cells retain their nuclei. These erythrocytes rank among the most extreme examples of cell specialization and gene repression known. The nuclei of avian erythrocytes and others, contain a tissue-specific histone protein in addition to the more usual complement of vertebrate histone. This histone (H5, V, F2c) has been extensively investigated with a view to linking its presence to structural and molecular changes involved in the condensation and repression of red cell nuclei. The evidence to dat suggests that H5, in conjunction with tissue-specific changes in non-histone proteins, may be responsible for keeping the genomes of nucleated erythrocytes permanently inactive.