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Background: Transposable elements are mobile DNA repeat sequences, known to have high impact on genes, genome structure and evolution. This has stimulated broad interest in the detailed biological studies of transposable elements. Hence, we have developed an easy-to-use tool for the comparative analysis of the structural organization and functional relationships of transposable elements, to help understand their functional role in genomes. Results: We named our new software VisualTE and describe it here. VisualTE is a JAVA stand-alone graphical interface that allows users to visualize and analyze all occurrences of transposable element families in annotated genomes. VisualTE reads and extracts transposable elements and genomic information from annotation and repeat data. Result analyses are displayed in several graphical panels that include location and distribution on the chromosome, the occurrence of transposable elements in the genome, their size distribution, and neighboring genes' features and ontologies. With these hallmarks, VisualTE provides a convenient tool for studying transposable element copies and their functional relationships with genes, at the whole-genome scale, and in diverse organisms. Conclusions: VisualTE graphical interface makes possible comparative analyses of transposable elements in any annotated sequence as well as structural organization and functional relationships between transposable elements and other genetic object. This tool is freely available at: http://lcb.cnrs-mrs.fr/spip.php?article867. [ABSTRACT FROM AUTHOR]

Marine planktonic archaea are widespread and abundant in deep oceanic waters but, despite their obvious ecological importance, little is known about them. Metagenomic analyses of large genome fragments allow access to both gene content and genome structure from single individuals of these cultivation-reluctant organisms. We present the comparative analysis of 22 archaeal genomic clones containing 16S rRNA genes that were selected from four metagenomic libraries constructed from meso- and bathypelagic plankton of different oceanic regions (South Atlantic, Antarctic Polar Front, Adriatic and Ionian Sea; depths from 500 to 3000 m). We sequenced clones of the divergent archaeal lineages Group 1A (Crenarchaeota) and Group III (Euryarchaeota) as well as clones from the more frequent Group I Crenarchaeota and Group II Euryarchaeota. Whenever possible, we analysed clones that had identical or nearly identical 16S rRNA genes and that were retrieved from distant geographical locations, that is, that defined pan-oceanic operational taxonomic units (OTUs). We detected genes involved in nitrogen fixation in Group 1A Crenarchaeota, and genes involved in carbon fixation pathways and oligopeptide importers in Group I Crenarchaeota, which could confirm the idea that these are mixotrophic. A two-component system resembling that found in ammonia-oxidizing bacteria was found in Group III Euryarchaeota, while genes for anaerobic respiratory chains were detected in Group II Euryarchaeota. Whereas gene sequence conservation was high, and recombination and gene shuffling extensive within and between OTUs in Group I Crenarchaeota, gene sequence conservation was low and global synteny maintained in Group II Euryarchaeota. This implies remarkable differences in genome dynamics in Group I Crenarchaeota and Group II Euryarchaeota with recombination and mutation being, respectively, the dominant genome-shaping forces. These observations, along with variations in GC content, led us to hypothesize that the two groups of organisms have fundamentally different lifestyles.The ISME Journal (2008) 2, 865–886; doi:10.1038/ismej.2008.40; published online 8 May 2008 [ABSTRACT FROM AUTHOR]

Identifying the mechanisms of eukaryotic genome evolution by comparative genomics is often complicated by the multiplicity of events that have taken place throughout the history of individual lineages, leaving only distorted and superimposed traces in the genome of each living organism. The hemiascomycete yeasts, with their compact genomes, similar lifestyle and distinct sexual and physiological properties, provide a unique opportunity to explore such mechanisms. We present here the complete, assembled genome sequences of four yeast species, selected to represent a broad evolutionary range within a single eukaryotic phylum, that after analysis proved to be molecularly as diverse as the entire phylum of chordates. A total of approximately 24,200 novel genes were identified, the translation products of which were classified together with Saccharomyces cerevisiae proteins into about 4,700 families, forming the basis for interspecific comparisons. Analysis of chromosome maps and genome redundancies reveal that the different yeast lineages have evolved through a marked interplay between several distinct molecular mechanisms, including tandem gene repeat formation, segmental duplication, a massive genome duplication and extensive gene loss. [ABSTRACT FROM AUTHOR]

Background: Numerous DNA microarray hybridization experiments have been performed in yeast over the last years using either synthetic oligonucleotides or PCR-amplified coding sequences as probes. The design and quality of the microarray probes are of critical importance for hybridization experiments as well as subsequent analysis of the data. Results: We present here a novel design of Saccharomyces cerevisiae microarrays based on a refined annotation of the genome and with the aim of reducing cross-hybridization between related sequences. An effort was made to design probes of similar lengths, preferably located in the 3'-end of reading frames. The sequence of each gene was compared against the entire yeast genome and optimal sub-segments giving no predicted cross-hybridization were selected. A total of 5660 novel probes (more than 97% of the yeast genes) were designed. For the remaining 143 genes, cross-hybridization was unavoidable. Using a set of 18 deletant strains, we have experimentally validated our cross-hybridization procedure. Sensitivity, reproducibility and dynamic range of these new microarrays have been measured. Based on this experience, we have written a novel program to design long oligonucleotides for microarray hybridizations of complete genome sequences. Conclusions: A validated procedure to predict cross-hybridization in microarray probe design was defined in this work. Subsequently, a novel Saccharomyces cerevisiae microarray (which minimizes cross-hybridization) was designed and constructed. Arrays are available at Eurogentec S. A. Finally, we propose a novel design program, OliD, which allows automatic oligonucleotide design for microarrays. The OliD program is available from authors. [ABSTRACT FROM AUTHOR]

There is increasing evidence that DNA duplication is a common and ongoing process that plays a major role in molecular evolution of genomes and that a large fraction of the duplicated gene copies becomes non-functional by accumulation of deleterious mutations. In order to describe this phenomenon, we systematically searched the 6404 intergenic regions (IRs) of the genome of Saccharomyces cerevisiae for traces of coding sequences presenting degenerated but still recognizable sequence similarity with active open reading frames (5823 annotated ORFs). We detected a total of 124 anciently coding regions, or “gene relics”, showing similarity to a total of 149 distinct active ORFs. This set of relics shows a continuum of sequence degeneration from those whose sequence is slightly altered compared to the functional ORF (classically defined as pseudogenes), to those that contains so many deleterious mutations, as to reach the limit of recognition. Gene relics are more concentrated in the subtelomeric regions of the chromosomes, reflecting the high plasticity of these regions. The presence of relics also revealed ancestral duplication events of chromosomal segments that were previously undetected. Some of these segments are intermingled with the more easily recognizable ancestral blocks of duplication, indicating successive duplication events. We present a compilation of all the data available, leading to a total of 278 pseudogenes in the genome of S. cerevisiae. [Copyright &y& Elsevier]