A new family of transcriptional regulators of tungstoenzymes and molybdate/tungstate transport.

Bacterial genes for molybdenum-containing and tungsten-containing enzymes are often differentially regulated depending on the metal availability in the environment. Here, we describe a new family of transcription factors with an unusual DNA-binding domain related to excisionases of bacteriophages. These transcription factors are associated with genes for various molybdate and tungstate-specific transporting systems as well as molybdo/tungsto-enzymes in a wide range of bacterial genomes. We used a combination of computational and experimental techniques to study a member of the TF family, named TaoR (for tungsten-containing aldehyde oxidoreductase regulator). In Desulfovibrio vulgaris Hildenborough, a model bacterium for sulfate reduction studies, TaoR activates expression of aldehyde oxidoreductase aor and represses tungsten-specific ABC-type transporter tupABC genes under tungsten-replete conditions. TaoR binding sites at aor promoter were identified by electrophoretic mobility shift assay and DNase I footprinting. We also reconstructed TaoR regulons in 45 Deltaproteobacteria by comparative genomics approach and predicted target genes for TaoR family members in other Proteobacteria and Firmicutes.

Rex (encoded by DVU_0916) in Desulfovibrio vulgaris Hildenborough is a repressor of sulfate adenylyl transferase and is regulated by NADH.

Although the enzymes for dissimilatory sulfate reduction by microbes have been studied, the mechanisms for transcriptional regulation of the encoding genes remain unknown. In a number of bacteria the transcriptional regulator Rex has been shown to play a key role as a repressor of genes producing proteins involved in energy conversion. In the model sulfate-reducing microbe Desulfovibrio vulgaris Hildenborough, the gene DVU_0916 was observed to resemble other known Rex proteins. Therefore, the DVU_0916 protein has been predicted to be a transcriptional repressor of genes encoding proteins that function in the process of sulfate reduction in D. vulgaris Hildenborough. Examination of the deduced DVU_0916 protein identified two domains, one a winged helix DNA-binding domain common for transcription factors, and the other a Rossman fold that could potentially interact with pyridine nucleotides. A deletion of the putative rex gene was made in D. vulgaris Hildenborough, and transcript expression studies of sat, encoding sulfate adenylyl transferase, showed increased levels in the D. vulgaris Hildenborough Rex (RexDvH) mutant relative to the parental strain. The RexDvH-binding site upstream of sat was identified, confirming RexDvH to be a repressor of sat. We established in vitro that the presence of elevated NADH disrupted the interaction between RexDvH and DNA. Examination of the 5' transcriptional start site for the sat mRNA revealed two unique start sites, one for respiring cells that correlated with the RexDvH-binding site and a second for fermenting cells. Collectively, these data support the role of RexDvH as a transcription repressor for sat that senses the redox status of the cell.

Pro-Frame: similarity-based gene recognition in eukaryotic DNA sequences with errors.

Performance of existing algorithms for similarity-based gene recognition in eukaryotes drops when the genomic DNA has been sequenced with errors. A modification of the spliced alignment algorithm allows for gene recognition in sequences with errors, in particular frameshifts. It tolerates up to 5% of sequencing errors without considerable drop of prediction reliability when a sufficiently close homologous protein is available (normalized evolutionary distance similarity score 50% or higher).

Gene recognition in eukaryotic DNA by comparison of genomic sequences.

MOTIVATION: Sequencing of complete eukaryotic genomes and large syntenic fragments of genomes makes it possible to apply genomic comparison for gene recognition. RESULTS: This paper describes a spliced alignment algorithm that aligns candidate exon chains of two homologous genomic sequence fragments from different species. The algorithm is implemented in Pro-Gen software. Unlike other algorithms, Pro-Gen does not assume conservation of the exon-intron structure. Amino acid sequences obtained by the formal translation of candidate exons are aligned instead of nucleotide sequences, which allows for distant comparisons. The algorithm was tested on a sample of human-mammal (mouse), human-vertebrate (Xenopus ) and human-invertebrate (Drosophila ) gene pairs. Surprisingly, the best results, 97-98% correlation between the actual and predicted genes, were obtained for more distant comparisons, whereas the correlation on the human-mouse sample was only 93%. The latter value increases to 95% if conservation of the exon-intron structure is assumed. This is caused by a large amount of sequence conservation in non-coding regions of the human and mouse genes probably due to regulatory elements. AVAILABILITY: Pro-Gen v. 3.0 is available to academic researchers free of charge at http://www.anchorgen.com/pro_gen/pro_gen.html.

Comparative analysis of regulatory patterns in bacterial genomes.

Recognition of transcription regulatory sites in bacterial genomes is a notoriously difficult problem. There are no algorithms capable of making reliable predictions even for well-studied sites such as the CRP (cyclic AMP receptor protein) box. However, availability of complete bacterial genomes makes it possible to make reliable predictions with bad rules. This comparative approach is based on the assumption that sets of co-regulated genes are conserved in related bacteria. Thus true sites occur upstream of orthologous genes, whereas false candidates are scattered at random. This means not only that knowledge about regulation in well-studied genomes can be transferred to newly sequenced ones, but also that new members of regulons can be found. This paper reviews several recent studies. In particular, a detailed analysis of catabolite repression in gamma-purple bacteria is presented.