Global expression mapping of mammalian genomes

he aim of genome projects is to decipher all the information contained within the DNA of an organism and to study the way this information is processed in physiological processes. It is believed that more than 95% of the information content of the mammalian genome is represented in the protein coding sequences that make up only approximately 2% of the DNA sequence. Consequently much effort is being invested in the study of coding sequences in the form of cDNA analysis. This thesis is concerned with the development of a new strategy for a highly parallel approach to analyse entire cDNA libraries. The strategy is based upon generating sufficient sequence information to identify uniquely more than 100,000 cDNA clones by hybridisation with short oligonucleotides, typically 7 - 10 mers. Each oligonucleotide is hybridised to all cDNA clones in parallel and under stringent conditions positively identifies a subset (3 - 10%) of clones. Oligonucleotides are designed in such a way that each will positively identify a different subset of clones and statistical simulations estimate that approximately 200 such hybridisation events are required to identify uniquely upto 100,000 cDNA sequences. Such a fingerprint can be generated from many cDNA libraries constructed from different tissue mRNAs and will not only lead to the identification of most sequecnes expressed from the genome but also indicate the level of expression by determining the number of times any given sequence is represented across different cDNA libraries. A human foetal brain cDNA library has been constructed and 100,000 clones arrayed into microtitre plates and on nylon membranes. All the required technological developments have been carried out successfully and are presented. In excess of 200 oligonucleotide hybridisations have been performed on a subset of 32,000 cDNA clones and 1,000 sequenced control clones. A detailed analysis of the data on the control clones is presented and the implications for cDNA fingerprinting discussed

Rapid identification of new transcribed human sequences: a semi-ordered approach

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A set of ligation-independent in vitro translation vectors for eukaryotic protein production

<p>Abstract</p> <p>Background</p> <p>The last decade has brought the renaissance of protein studies and accelerated the development of high-throughput methods in all aspects of proteomics. Presently, most protein synthesis systems exploit the capacity of living cells to translate proteins, but their application is limited by several factors. A more flexible alternative protein production method is the cell-free in vitro protein translation. Currently available in vitro translation systems are suitable for high-throughput robotic protein production, fulfilling the requirements of proteomics studies. Wheat germ extract based in vitro translation system is likely the most promising method, since numerous eukaryotic proteins can be cost-efficiently synthesized in their native folded form. Although currently available vectors for wheat embryo in vitro translation systems ensure high productivity, they do not meet the requirements of state-of-the-art proteomics. Target genes have to be inserted using restriction endonucleases and the plasmids do not encode cleavable affinity purification tags.</p> <p>Results</p> <p>We designed four ligation independent cloning (LIC) vectors for wheat germ extract based in vitro protein translation. In these constructs, the RNA transcription is driven by T7 or SP6 phage polymerase and two TEV protease cleavable affinity tags can be added to aid protein purification. To evaluate our improved vectors, a plant mitogen activated protein kinase was cloned in all four constructs. Purification of this eukaryotic protein kinase demonstrated that all constructs functioned as intended: insertion of PCR fragment by LIC worked efficiently, affinity purification of translated proteins by GST-Sepharose or MagneHis particles resulted in high purity kinase, and the affinity tags could efficiently be removed under different reaction conditions. Furthermore, high in vitro kinase activity testified of proper folding of the purified protein.</p> <p>Conclusion</p> <p>Four newly designed in vitro translation vectors have been constructed which allow fast and parallel cloning and protein purification, thus representing useful molecular tools for high-throughput production of eukaryotic proteins.</p

An investigation into the serological and molecular diagnosis of Jaagsiekte Sheep Retrovirus (JSRV)

Thesis (M.Med.)-University of KwaZulu-Natal, 2005.The Jaagsiekte Sheep Retrovirus (JSRV), an exogenous type B/D-retrovirus with about 10-15 endogenous counterparts in all normal sheep genomes, causes Jaagsiekte (JS) or ovine pulmonary adenocarcinoma (OPA), a contagious lung cancer of sheep. This sheep lung cancer has been identified as the best natural out-bred model that can be used to study human epithelial tumours. The close similarity between the pathology of the sheep disease and Human Bronchiolo-alveolar carcinoma are highly suggestive that the human disease could have a similar aetiology and mechanism to the sheep disease. However, in the case of sheep at the time of the study there was a need for an assay that could be used to screen for infected sheep. The isolation, cloning and subsequent sequencing of the first full-length exogenous and endogenous forms of JSRV contributed greatly towards JSRV research. Until recently the diagnosis of OPA was based mostly on clinical presentation with confirmation by micro and macro examination of the affected lungs by expert pathologists. In the absence of a specific humoral response no serology-based tests were available to diagnose the disease early in live animals. Control and management of the disease was primarily by regular flock inspections and prompt culling of the suspected cases. The objective of this research project was therefore to assess and investigate the serological and molecular diagnosis of JSRV. In an attempt to develop a serology based assay three proteins were identified as candidate diagnostic antigens, the group specific antigen JSRV p26, the transmembrane and the orf-X proteins. Genes coding for all three proteins were isolated, cloned and expressed. The JSRV p26 was sufficiently purified and its potential as a diagnostic antigen was evaluated in both a Western blot and ELISA. Our studies confirmed that there were no circulating antibodies to the JSRV capsid protein. Evidence suggested that the immune response was localised to the lungs. Lung lavage samples were therefore collected from infected and normal sheep and analysed for the presence of JSRV p26 antibodies using an in-house JSp26 peroxidase conjugate in an antigen capture assay. This assay lacked sensitivity but the results indicated that there was a specific localised immune response to JSRV in the lungs of OPA affected sheep. This was confirmed with an in-house antigen capture assay that we developed. JS antigen was detected in the lung and nasal fluid of affected sheep, but not in equivalent samples from normal sheep. Three molecular assays were investigated for their sensitivity and specificity, the LTR-gag PCR, U3/LTR hemi-nested PCR and the PCR that covered the V1/V2 region. The U3/LTR hemi-nested assay was 2 logs more sensitive than the LTR-gag PCR. However, it detected the endogenous JSRV5.9A1 loci at higher concentrations. This was overcome by designing a more specific primer P3M for the first step of the U3/LTR hemi-nested PCR and the use of the AmpliTaq Gold DNA polymerase. This assay proved to be both sensitive and specific enough to screen for the infectious exogenous JSRV in peripheral blood samples from individual sheep. It is now possible to use this assay to selectively eradicate the disease from a flock through a selective culling programme. Furthermore, the assay could be made quantitative by the inclusion of concentration standards

Understanding the role of different strain types of Fusobacterium necrophorum: biofilms, glycans and metabolic pathways

Fusobacterium necrophorum an obligate Gram-negative anaerobe has been implicated in the cause of persistent severe throat infections and the systemic life-threatening Lemierre’s syndrome; a potentially fatal periodontal disease, which results in abscess formation in the tonsils. The use of antibiotics had led to decreased incidence of F. necrophorum infections to a point that the bacterium became a forgotten pathogen; however, there has recently been a rise in interest. F. necrophorum is thought to survive the aerobic oropharynx by biofilm formation. Studies of optimal conditions for biofilm formation could be useful in improving therapeutic options. This current study determined that strains ARU 01 and JCM 3718 formed the most biofilm at 37 °C, with reduction in biofilm observed at 26 °C and 42 °C. Strain JCM 3724 on the other hand, formed most biofilm at 26 °C and 42 °C; this is an indication that strain JCM 3724 but not JCM 3718 or ARU 01 was able to survive in extreme temperatures by forming biofilms; all strains produced more biofilm at pH 4. Biofilm formation was observed in both mono and dual species culture of F. necrophorum, in dual culture the organisms became resistant to penicillin and ciprofloxacin. As glycans are implicated in biofilm formation, bacterial adhesion to host cells and pathogenicity, the cell surface glycans and cell extracts of F. necrophorum were investigated using enzyme-linked lectin assays (ELLA) and lectin histochemical staining. No significant differences were seen in the staining patterns, but a patchy and variable staining was noted for Sambucus nigra that detects sialic acid. A surface lectin, the Galactose binding protein was identified and characterised as binding to unsubstituted beta galactosyl residues of the type carried by many bacteria suggesting a role in biofilm formation. Subsequent molecular and bioinformatic studies identified all but one key component of the lipid A pathway; lpxI was shown to substitute for lpxH in the pathway. The component genes required for expression of sialic acid on the cell surface of the organism were determined; a polymorphism, the presence or absence of siaA, suggested some but not all strains had the ability to express this sugar on the cell surface. Further studies are required to determine whether this is linked to pathogenicity. Genomic and proteomic studies on type strains and clinical isolates revealed significant differences between subsp. necrophorum and funduliforme that will be useful in developing a simple molecular based subspeciation test. The subsp. funduliforme was split into 3 clusters (A, B and C) based on the genomic data; proteomic studies were used to determine the impact of the non-synonymous SNPs seen; two clusters were observed at the protein level, A and B+C. Most of the amino acid replacements that differentiated the clusters A from B +C were conservative or semi- conservative; more differences were noted between the two subspecies and these also included non-conservative changes that could affect protein structure and function. Clearly, there is scope for further work to elucidate the evolution of these clusters and their relevance to pathogenicity