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Results for “gene expression evolution”

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At least 433 records · Page 24Linked to original sources
PubMed2004

Directed evolution of pyruvate decarboxylase-negative Saccharomyces cerevisiae, yielding a C2-independent, glucose-tolerant, and pyruvate-hyperproducing yeast.

The absence of alcoholic fermentation makes pyruvate decarboxylase-negative (Pdc(-)) strains of Saccharomyces cerevisiae an interesting platform for further metabolic engineering of central metabolism. However, Pdc(-) S. cerevisiae strains have two growth defects: (i) growth on synthetic medium in glucose-limited chemostat cultures requires the addition of small amounts of ethanol or acetate and (ii) even in the presence of a C(2) compound, these strains cannot grow in batch cultures on synthetic medium with glucose. We used two subsequent phenotypic selection strategies to obtain a Pdc(-) strain without these growth defects. An acetate-independent Pdc(-) mutant was obtained via (otherwise) glucose-limited chemostat cultivation by progressively lowering the acetate content in the feed. Transcriptome analysis did not reveal the mechanisms behind the C(2) independence. Further selection for glucose tolerance in shake flasks resulted in a Pdc(-) S. cerevisiae mutant (TAM) that could grow in batch cultures ( micro (max) = 0.20 h(-1)) on synthetic medium, with glucose as the sole carbon source. Although the exact molecular mechanisms underlying the glucose-tolerant phenotype were not resolved, transcriptome analysis of the TAM strain revealed increased transcript levels of many glucose-repressible genes relative to the isogenic wild type in nitrogen-limited chemostat cultures with excess glucose. In pH-controlled aerobic batch cultures, the TAM strain produced large amounts of pyruvate. By repeated glucose feeding, a pyruvate concentration of 135 g liter(-1) was obtained, with a specific pyruvate production rate of 6 to 7 mmol g of biomass(-1) h(-1) during the exponential-growth phase and an overall yield of 0.54 g of pyruvate g of glucose(-1).

Culture Media↗
PubMed1995

Streptococcus salivarius ATCC 25975 possesses at least two genes coding for primer-independent glucosyltransferases.

Fractionation of the culture medium showed that Streptococcus salivarius ATCC 25975 secreted a glucosyltransferase (Gtf) that was primer independent. On the basis of this observation, a gene library of S. salivarius chromosomal DNA cloned into lambda L47.1 was screened for a gene(s) coding for such an activity. As a result of this screening process, two new gtf genes, gtfL and gtfM, both of which coded for primer-independent Gtf activities, were isolated. GtfL produced an insoluble glucan that was refractory to digestion by the endo-(1-->6)-alpha-D-glucanase. of Chaetonium gracile, while GtfM produced a soluble glucan that was readily degraded by the glucanase. Comparison of the deduced amino acid sequences of gtfL and gtfM with 10 other available Gtf sequences allowed the relatedness of the conserved catalytic regions to be assessed. This analysis showed that the 12 enzymes did not form clusters based on their primer dependencies or on their product solubilities. Further analysis of the YG repeats in the C-terminal glucan-binding domains of GtfJ, GtfK, GtfL, and GtfM from S. salivarius showed that there was strong homology between a block of contiguous triplet YG repeats present in the four alleles. These blocks of YG repeats were coded for by a region of each gene that appeared to have arisen as a result of a recent duplication event(s).

Amino Acid Sequence↗
PubMed2003

Cardiac chamber formation: development, genes, and evolution.

Concepts of cardiac development have greatly influenced the description of the formation of the four-chambered vertebrate heart. Traditionally, the embryonic tubular heart is considered to be a composite of serially arranged segments representing adult cardiac compartments. Conversion of such a serial arrangement into the parallel arrangement of the mammalian heart is difficult to understand. Logical integration of the development of the cardiac conduction system into the serial concept has remained puzzling as well. Therefore, the current description needed reconsideration, and we decided to evaluate the essentialities of cardiac design, its evolutionary and embryonic development, and the molecular pathways recruited to make the four-chambered mammalian heart. The three principal notions taken into consideration are as follows. 1) Both the ancestor chordate heart and the embryonic tubular heart of higher vertebrates consist of poorly developed and poorly coupled "pacemaker-like" cardiac muscle cells with the highest pacemaker activity at the venous pole, causing unidirectional peristaltic contraction waves. 2) From this heart tube, ventricular chambers differentiate ventrally and atrial chambers dorsally. The developing chambers display high proliferative activity and consist of structurally well-developed and well-coupled muscle cells with low pacemaker activity, which permits fast conduction of the impulse and efficacious contraction. The forming chambers remain flanked by slowly proliferating pacemaker-like myocardium that is temporally prevented from differentiating into chamber myocardium. 3) The trabecular myocardium proliferates slowly, consists of structurally poorly developed, but well-coupled, cells and contributes to the ventricular conduction system. The atrial and ventricular chambers of the formed heart are activated and interconnected by derivatives of embryonic myocardium. The topographical arrangement of the distinct cardiac muscle cells in the forming heart explains the embryonic electrocardiogram (ECG), does not require the invention of nodes, and allows a logical transition from a peristaltic tubular heart to a synchronously contracting four-chambered heart. This view on the development of cardiac design unfolds fascinating possibilities for future research.

Animals↗
PubMed2004

Deconstructing the genesis of animal form.

Santa Fe - with its museums and galleries full of art and crafts inspired by natural forms - was the perfect setting for a Keystone conference on vertebrate organogenesis in February 2004. Organized by Gail Martin and Cliff Tabin, the conference sessions were loosely subdivided into anatomical systems - 'skin, hair, teeth', 'pancreas, liver, gut', 'skeleton', and so on. However, from the outset, common themes emerged that transcended particular organ systems and generated a sense of unity and excitement among the participants.

Animals↗
PubMed1995

Is thermophily a transferrable property in bacteria?

Bacteria exhibit unique diversity in their ability to grow at different temperatures. Indeed, eubacteria and archaebacteria are the only organisms able to grow above 65 degrees C. The temperature range for a species is generally considered to be a stable character; however, mutants may be isolated that have a Tmin or Tmax below or above the parent organism. Some bacteria may also be coaxed to grow at different temperature by training cultures, through an incremental increase or decrease of temperature. Genetic approaches, for example, the transformation of mesophilic Bacillus to thermophily using DNA from closely related thermophiles, has been very controversial. A major problem has been the lack of stability of the high-temperature phenotype upon subculture, which has not allowed extensive genetic and biochemical characterization of the transformants. The mechanism whereby the thermophilic phenotype is carried is unknown, although it is possible that the adapter genes are plasmid encoded. Studies using phenotypically stable transformants indicated that the thermostability of some cellular components was significantly increased, both in the vegetative cell and spore state. Enzyme thermostability, for example, appeared to be associated with an increased use of hydrophobic amino acids; however, the biochemical mechanisms for these alterations remain unknown. Thermophily is still a challenging problem with some interesting molecular biology.

Adaptation, Physiological↗
PubMed1998

Maize as a model system for investigating the molecular basis of morphological evolution in plants.

The genetic and molecular bases of morphological evolution in plants are largely unknown. To address questions surrounding this issue, my laboratory has been investigating the evolution of maize from its wild ancestor, teosinte. Our research suggests that a few gene changes of large effect were involved in the evolution of several different traits including plant and ear architecture and kernel color. In cases where gene function could be identified, the genes involved in maize evolution were regulatory in nature. Additional evidence suggests that changes in cis regulatory elements of the regulatory genes rather than changes in protein function underlie the evolution of the traits analyzed. Future work with other plant species, especially wild plants, will be required to test the generality of our observations with maize.

Biological Evolution↗
PubMed2002

[Production of bacteriocins by gram-positive bacteria and the mechanisms of transcriptional regulation].

The mechanisms of production of bacteriocins in Gram-positive bacteria and the main distinctions of these bacteriocins from the bacteriocins of Gram-negative bacteria (colicins) are outlined. A classification of antibacterial peptides is presented, and most of known class I and II peptides are pointed out. In Gram-positive bacteria, the cases of bacteriocin-associated quorum sensing are examined. For these cases, the structure of loci containing the genes of regulatory systems, transport, immunity, processing, and posttranslational modification of antibacterial peptides are described. All known regulatory sites for class II bacteriocins are presented. A description of the putative regulatory sites found by us and their classification are provided. The evolutionary tree of transcriptional response regulators is shown to correspond to the tree of their recognition sites.

Bacteriocins↗
PubMed2003

Exploiting genome data to understand the function, regulation, and evolutionary origins of toxicologically relevant genes.

The wealth of new information coming from the many genome sequencing projects is providing unprecedented opportunities for major advances in all areas of biology, including the environmental health sciences. To facilitate this discovery process, experts in the fields of functional genomics and informatics and the emerging field of toxicogenomics recently gathered at the Mount Desert Island Biological Laboratory in Salisbury Cove, Maine, site of a National Institute of Environmental Health Sciences Marine and Freshwater Biomedical Science Center, to share their ideas and latest research findings. The goal of the symposium was to highlight approaches that may be used to identify and characterize toxicologically relevant genes being discovered in the genome sequencing projects. Many of the approaches rely heavily on comparative models as a way of identifying gene homology, ontology, and physiologic function, and on the availability of databases that facilitate storage, analysis, interpretation, and widespread dissemination of relevant data.

Animals↗
PubMed1992

Steroid receptors.

Explore the source record for details and available documents.

Binding Sites↗