La tesi esta basada en l'adaptació de l'ús de codons a genomes procariotes, especialment l'adaptació de l'ús de codons a una alta expressió. Hi ha un grup de genomes procariotes, els quals estan sota una selecció traduccional, que tenen un grup de gens amb un ús de codons esbiaixat de la resta de gens del genoma i adaptats a l'abundància dels tRNA. Hem desenvolupat un nou algoritme per a avaluar si un genoma esta sota selecció traduccional i predir els gens altament expressat de tots els genomes sota selecció traduccional. Aquestes prediccions són públiques a la base de dades HEG-DB (http://genomes.urv.cat/HEG-DB), la qual s'ha publicat a la revista Nucleic Acids Research. Les prediccions de gens altament expressats s'han fet servir com a filtre en les prediccions de gens adquirits per transferència horitzontal, ja que els gens altament expressats molts cops son predits com a falsos positius en la predicció de gens adquirits. Amb les dades de la predicció de gens altament expressats, també hem desenvolupat una nova eina Bioinformàtica, anomenada OPTIMIZER (http://genomes.urv.cat/OPTIMIZER) i publicada al Nucleic Acids Research, per tal d'optimitzar l'ús de codons d'un gen per a incrementar la seva expressió en experiments d'expressió heteròloga de proteïnes. També hem estudiat un cas particular d'adaptació de l'ús de codons. El cas de l' 'amelioration', que és l'adaptació de l'ús de codons que pateix un gen inserit en un genoma hoste. Aquest cas l'hem estudiat amb els gens mitocondrials que varen saltar al genoma nuclear i varen haver d'adaptar el seu us de codons mitocondrial a l'ús de codons del genoma nuclear. Per tal d'estudiar l''amelioration', hem desenvolupat un nou índex anomenat CAI esperat (eCAI) i una nova eina Bioinformàtica anomenada CAIcal (http://genomes.urv.cat/CAIcal), que està en procés de revisió a la revista BMC Bioinformatics. Analitzant l'anàlisi de l'ús de codons dels genomes completament sequenciats vàrem realitzar una troballa que s'aparta una mica del tema central de la tesi. Vàrem veure que els genomes que estan adaptats a la (hiper)termofília tenen un patró de l'ús de codons i d'aminoàcids diferent a la resta de genomes (mesòfils). Aquest fet ens ha permès descobrir casos de guany i pèrdua (recents i antics) de la capacitat d'adaptació termofílica en genomes procariotes. Aquests resultats han donat lloc a una publicació a la revista Trends in Genetics. Durant la tesi he realitzat una estada de 4 mesos (Febrer - Juny, 2006) en el laboratori de bioinformàtica del departament de biologia de la universitat nacional d'Irlanda a Maynooth sota la supervisió del Dr James McInerney on vaig desenvolupar un nou programa per a la comparació d'arbres filogenètics anomenat TOPD/FMTS (http://genomes.urv.cat/topd) el qual està publicat a la revista Bioinformatics. / This thesis is based in codon usage adaptation in prokaryotic genomes, especially the codon usage adaptation to a high expression. In genomes under translational selection, the group of highly expressed genes has a codon usage adapted to the most abundant tRNA species. We have developed a new iterative algorithm which predicts a group of highly expressed genes in genomes under translational selection by using the Codon Adaptation Index and the group of ribosomal protein genes as a seed. We have developed a new genomic database, called HEG-DB, to store genes that are predicted as highly expressed in prokaryotic complete genomes under strong translational selection. The database is freely available at http://genomes.urv.cat/HEG-DB and it has been published in Nucleic Acids Research. The predicted highly expressed genes are used as an initial filter to reduce the number of false positives of the Horizontal Gene Transfer Database, due to highly expressed genes are usually false positive in predictions of acquired genes. We have developed a new web sever, called OPTIMIZER (http://genomes.urv.cat/OPTIMIZER), which has been published in Nucleic Acids Research, to optimize the codon usage of DNA or RNA sequences. This new web server can be used to predict and optimize the level expression of a gene in heterologous gene expression or to express new genes that confer new metabolic capabilities in a given species. We have also analyzed an especial case of codon usage adaptation, which is called 'amelioration'. The 'amelioration' is the adaptation of foreign genes to a new genome. This is the case of mitochondrial genes encoded in the human nuclear genome and originally encoded in the proto-mitochondria. To test the 'amelioration' process we have developed an expected value of CAI (eCAI) to find out whether the differences in the CAI are statistically significant or whether they are the product of biased nucleotide and/or amino acid composition and a new bioinformatics tool called CAIcal (http://genomes.urv.cat/CAIcal). We have also analyzed the evolution of thermophilic adaptation in prokaryotes and we suggest that the amino acid composition signature in thermophilic organisms is a consequence of or an adaptation to living at high temperatures, not its cause. Our findings suggest that there have been several cases where the capacity for thermophilic adaptation has been gained or lost throughout the evolution of prokaryotes. These results have been published in Trends in Genetics. During my thesis I have worked for four months in the Bioinformatics Laboratory of the Biology Department at the National University of Ireland under the supervision of Dr James O. McInerney where I developed a new software program to compare phylogenetic trees called TOPD/FMTS (http://genomes.urv.cat/topd), that has been published in Bioinformatics.

A metagenome originated from a shotgun sequencing of a microbial community is a heterogeneous mixture of rather short sequences. A vast majority of microbial species in a given community (99%) are likely to be non-cultivable. Many protein-coding regions in a new metagenome are likely to code for barely detectable homologs of already known proteins. Therefore, an ab initio method that would accurately identify the new genes is a vitally important tool of metagenomic sequence analysis. However, a heuristic model method for finding genes in short prokaryotic sequences with anonymous origin was proposed in 1999 prior to the advent of metagenomics. With hundreds of new prokaryotic genomes available it is now possible to enhance the original approach and to utilize direct polynomial and logistic approximations of oligonucleotide frequencies. The idea was to bypass traditional ways of parameter estimation such as supervised training on a set of validated genes or unsupervised training on an anonymous sequence supposed to contain a large enough number of genes. The codon frequencies, critical for the model parameterization, could be derived from frequencies of nucleotides observed in the short sequence. This method could be further applied for initializing the algorithms for iterative parameters estimation for prokaryotic as well as eukaryotic gene finders.

Engineered cellular systems are a promising avenue for production of a wide range of useful products including renewable fuels, commodity and specialty chemicals, industrial enzymes, and pharmaceuticals. Achieving this breadth of biological products is facilitated by the diversity of organisms found in nature. Using biological and engineering principles, this diversity can be harnessed to make efficient and renewable bio-based products. Such advancements rely upon our ability to modify host genetics and metabolism. This work focuses on the development of new biotechnological tools which enable cellular engineering, and the implementation of these tools in eukaryotic systems. Mammalian cell engineering has important implications in protein therapeutics and gene therapy. One major limitation, however, is the ability to predictably control gene expression. We address this challenge by examining critical aspects of gene expression in human cells. First, we evaluate the impact of selection markers, a common mammalian expression element, on cell line development. In doing so, we determine that Zeocin is the best selection agent for human cells. Next, we identify loci across the genome that support high level expression of recombinant DNA and demonstrate their advantage for stable integration. Finally, we optimize a Cre recombinase based methodology that enables efficient retargeting of genomic loci. Collectively, this work augments the current genetic toolbox for human cell lines. Beyond basic gene expression, there is interest in understanding global interactions within the cell and how they relate to phenomena including gene regulation, expression and disease states. Although our tools are not yet sufficient to study these phenomena in many hosts, methods can be developed in lower eukaryotes and then adapted for more complex hosts later. We demonstrated two methods in S. cerevisiae that utilize a systems-level approach to understand complex phenotypes. First, we developed condition-specific codon optimization that utilizes systems biology information to optimize gene sequence in a condition-specific manner. Additionally, we developed a Graded Dominant Mutant Approach which can be used to dissect multifunctional proteins, understand epigenetic factors, and quantitatively determine protein-DNA interactions. Both can be implemented in many cellular hosts and expand our ability to engineer complex phenotypes in eukaryotic cell systems.

Over a decade after the completion of the human genome, researchers around the world are still wondering what information is hidden in the genome. Although the sequences of all human genes are known, it is still almost impossible to determine much more than the primary protein structure from the coding sequence of a gene. As a result of that, the need for recombinantly produced proteins to study protein structure and function is greater than ever. The main objective of this thesis has been to improve protein production, particularly using Escherichia coli. To improve protein production in Escherichia coli there are a number of different parameters to consider. Two very important parameters in the process of protein production are transcription and translation. To study the influence of differences in transcription rate, target proteins with different characteristics were produced under control of three promoters of different strength (lacUV5, trc and T7). Analyzing the total amount of target protein as well as the amount of soluble protein demonstrated the benefits of using a strong promoter such as T7. However, protein production is also highly dependent on translational efficiency, and a drawback associated with the use of Escherichia coli as host strain is that codons rarely used in this host can have a negative effect on the translation. The influence of using a strain supplied with genes for rare codon tRNAs, such as Rosetta(DE3), instead of the standard host strain BL21(DE3), was therefore evaluated. By using Rosetta(DE3) an improved protein yield for many of the poorly produced proteins was achieved, but more importantly the protein purity was significantly increased for a majority of the proteins. For further understanding of the underlying causes of the positive effects of Rosetta(DE3), the improved purity was thoroughly studied. The cause of this improvement was explained by the fact that Rosetta(DE3) has a significantly better read through of the full sequence during translation and thereby less truncated versions of the full-length protein is formed.  Moreover, the effect of supplementation of rare tRNAs was shown to be highly dependent on the target gene sequence. Surprisingly, it was not the total number of rare codons that determined the benefit of using Rosetta(DE3), instead it was shown that rare arginine codons and to some extent also rare codon clusters had a much bigger impact on the final outcome. As a result of the increased interest in large-scale studies in the field of proteomics, the need for high-throughput protein production pipelines is greater than ever. For that purpose, a protein production pipeline that allows handling of nearly 300 different proteins per week was set up within the Swedish Human Protein Atlas project. This was achieved by major and minor changes to the original protocol including protein production, purification and analysis. By using this standard setup almost 300 different proteins can be produced weekly, with an overall success rate of 81%. To further improve the success rate it has been shown that by adding an initial screening step, prior high-throughput protein production, unnecessary protein production can be avoided. A plate based micro-scale screening protocol for parallel production and verification of 96 proteins was developed. In that, protein production was performed using the EnBase® cultivation technology followed by purification based on immobilized metal ion affinity chromatography. The protein products were finally verified using matrix-assisted laser desorption ionization time-of-flight MS. By using this method, proteins that will be poorly produced can be sorted out prior high-throughput protein production. / <p>QC 20131120</p>

The rates and patterns at which nucleotide substitutions occur vary significantly across the genome sequence of vertebrates. A prominent example is the difference in the rate of evolution of functional sequences versus nonfunctional (neutrally evolving) sequences, which is explained by the influence of natural selection on functional sequences. However, even within neutrally evolving sequences there is striking variation in the rates and patterns of nucleotide substitutions. Unraveling the underlying processes that induce this variation is necessary to understand the basic principles of variation in neutral substitution profiles, which in turn is crucial for the identification of regions in the genome where natural selection acts. This research question builds the main focus of the present thesis. I have studied the causes and consequences of variation in different patterns of nucleotide substitutions. In particular, I have investigated substitutional strand asymmetries in mammalian genes and could show that they result from the asymmetric nature of DNA replication and transcription. Comparative analysis of substitutional asymmetries then suggested that the organization of DNA replication and the level of transcription are conserved among mammals. Further, I have examined the variation in CpG mutation rate among human genes and could show that beside DNA methylation also GC content plays a decisive role in CpG mutability. In addition, I have studied the signatures of GC-biased gene conversion and its impact on the evolution of the GC isochore structure in chicken. By comparison of the results in chicken to previous results in human I found evidence that karyotype stability is critical for the evolution of GC isochores. Finally, beside the empirical studies, I have performed theoretical investigations of substitution rates in functional sequences. More precisely, I have explored the temporal dynamics of estimates of the ratio of non-synonymous to synonymous substitution rates dN/dS in a phylogentic-population genetic framework.

<p>Various types of genetic constructs are widely used as diagnostic, prophylactic, and therapeutic tools for human diseases. They are also the workhorse in biotech and pharmaceutical industry for production of therapeutic antibodies and proteins. Since the majority of the genetic constructs encode protein products, it is therefore of tremendous value to human health and the society that we could find a way to fine-tune and optimize genetic constructs and hence protein expression for achieving maximal potency or long-lasting effects in therapeutics or for obtaining highest yields in pharmaceutical protein production. However, for protein-coding genes to be expressed in a heterologous host, the coding sequences need to be optimized by using synonymous codons to achieve reasonable levels of expression, if at all. Since codon optimization is done in a protein-by-protein basis with respect to specific host organisms, tissue/cell types, even health conditions, and there is no set of standard rules to follow, this process is still very unpredictable and time-consuming.</p><p>This thesis presents the development of a feasible platform for solving the problem of optimizing regular and long DNA constructs for academic or industrial purposes through the development of a novel cloning method for complex gene libraries, and based on the library expression system constructed in such manner, a platform for high-throughput screening of codon-optimized and error-corrected proteins, and a novel protocol for screening long gene constructs which could be extremely difficult to achieve by using regular screening methods. This multi-step platform has the potential for studying the natural systems: how codon bias correlates to protein expression efficiency, for generating improved pharmaceutical proteins and enhanced DNA vaccines and for constructing improved genome libraries.</p> / Dissertation

Bacteriophages (hereafter referred as phages) can translate their mRNAs efficiently by maximizing the use of codons decoded by the most abundant tRNAs of their bacterial hosts. Translation efficiency directly influences phage fitness and evolution. Reengineered phages find application in controlling their host population in both health and industry. The objective of this thesis work is to examine the factors shaping codon choices of single stranded DNA (ssDNA) and double stranded DNA (dsDNA) Escherichia coli phages. In chapter two, we employed two indices, rRSCU (correlation in relative synonymous codon usage between phages and their hosts) and CAI (codon adaptation index) to measure codon adaptation in phages. None of the analyzed ssDNA phages encode tRNAs while some dsDNA phages encode their own tRNAs. Both rRSCU and CAI are negatively correlated with number of tRNA genes encoded by these dsDNA phages. We observed significantly greater rRSCU for dsDNA phages (without tRNAs) than ssDNA phages. In addition, we propose that ssDNA phages have evolved a novel codon adaptation strategy to overcome the disruptive effect of their high C→T mutation rates in codon adaptation with host. In chapter three, we formulated an index phi to measure selection by host translation machinery and to present explicit linear and nonlinear models to characterize the effect of C→T mutation and host-tRNA-mediated selection on phage codon usage. The effect of selection (phi) on codon usage is detectable in most dsDNA and ssDNA phage species. C→T mutations also interfere with nonsynonymous substitutions at second codon positions, especially in ssDNA phages. Strand asymmetry along with the accompanying local variation in mutation bias can significantly affect codon adaptation in both dsDNA and ssDNA phages.

<p>RAS is a small GTPase that helps to convert extracellular cues into intracellular actions. It is the most commonly mutated oncogene and is found in an active mutant form in 90% of pancreatic cancers. Therefore, study of how this protein is made and then how this protein signals in the cell could provide the foundation for novel approaches to treat RAS-driven malignancies.</p><p>First I demonstrate that the level of protein expressed from the gene KRAS, but not the highly homologous gene HRAS, is limited in mammalian cells by an abundance of underrepresented (rare) codons in the encoding mRNA. KRAS mRNA from both ectopic plasmids as well as from the endogenous cellular gene is subject to slowed translation due to these rare codons within its coding sequence. This has consequences for tumorigenesis, as replacement of the rare codons with commonly used codons accelerates RAS driven tumor growth. This may extend beyond HRAS and KRAS, as many other homologous gene pairs show a high divergence in codon usage and protein expression, suggesting that this could be a wider phenomenon used by mammalian cells to regulate protein levels.</p><p>Second, I demonstrate that RAS driven tumors partially depend on eNOS for growth. Using genetically engineered mouse models that recapitulate the spontaneous development of pancreatic cancer, I demonstrate that the protein eNOS is progressively upregulated as tumors develop. I then demonstrate that genetic ablation of eNOS partially blocks the development of preinvasive pancreatic lesions in these mice, and trends toward increasing survival in mice that develop lethal pancreatic adenocarcinoma. Furthermore, I then show that inhibition of eNOS using the clinically tested small molecule L-NAME can also slow the development of preinvasive neoplasia and nonsignificantly increase survival, although not to the level of eNOS genetic ablation. These findings are applicable to a clinical setting, as in conjunction with others I show that L-NAME treatment of human pancreatic cancer xenografts halves their growth, even when the main side effect of L-NAME, hypertension, is treated.</p><p>Together, these studies provide a better understanding of how RAS functions within the cell, and thus, ultimately, how RAS driven cancers may be treated.</p> / Dissertation

Thesis (PhD)--Macquarie University, Division of Environmental & Life Sciences, Department of Biological Sciences, 2008. / Bibliography: p. 257-274. / Literature review -- General materials and methods -- Characterisation of strain collection -- Distribution of integrons and gene cassettes in pseudomonas -- Genomic context of pseudomonas integrons -- Evolutionary analysis of pseudomonas spp. integrons 199 -- Final discussion -- Appendix -- References. / Integrons associated with mobile genetic elements have played a central role in the emergence and spread of multiple antibiotic resistance in many pathogenic bacteria. However, the discovery of integrons in the chromosomes of diverse, non-pathogenic bacteria suggests that integrons have a broader role in bacterial evolution. The Pseudomonas stutzeri species complex is a well studied model for bacterial diversity. Members of the complex are genetically closely related, but sub-taxa are not able to be defined by exclusively shared sets of phenotypic characters. Rather, on the basis of total DNA:DNA similarity, Ps. stutzeri strains have been divided into 17 different groups (termed genomovars). Two Ps. stutzeri strains have been found to contain Chromosomal Integrons (CIs). This thesis involved exploration of the hypothesis that a CI was present in the common ancestor of the Ps. stutzeri species complex and assessed the impact of integrons on diversity across all Pseudomonads. The history and significance of integrons is discussed in Chapter 1 as part of a literature review, and general materials and methods are provided in Chapter 2. Chapters 3 - 6 comprise the sections in which data generated during my PhD project are presented. A comprehensive analysis of the relationships between the strains being analysed is presented in Chapter 3. In Chapter 4, results of PCR and hybridisation screening for integrons across the strain collection are presented. In Chapter 5 the recovery of additional integrons and in depth sequence analysis of the recovered integrons are described. Finally, Chapter 6 contains statistical analyses of integron-associated genes and Chapter 7 contains a final discussion the most significant findings. Twenty-three Pseudomonas spp. strains were screened for the presence of integrons. All but three were found to contain integron-like sequences; however, most integron sequences recovered contained inactivated core integrons. viii Despite having a chromosomal locus, integrons in Pseudomonas were found to have properties indicative of frequent horizontal transfer. Evidence was also obtained which suggests that integrons have been acquired at the same locus on multiple independent occasions. This has not been observed in other families of chromosomal integrons and suggests that the loci at which integrons in Pseudomonas are found are hotspots for recombination. / Mode of access: World Wide Web. / xiii, 274 p. ill

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 6 uppsatser.