Gapped BLAST and PSI-BLAST: a new generation of protein database search programs

GenBank

The GenBank(R) sequence database (http://www.ncbi.nlm.nih.gov/) incorporates DNA sequences from all available public sources, primarily through the direct submission of sequence data from individual laboratories and from large-scale sequencing projects. Most submitters use the BankIt (WWW) or Sequin programs to send their sequence data. Data exchange with the EMBL Data Library and the DNA Data Bank of Japan helps ensure comprehensive worldwide coverage. GenBank data is accessible through NCBI's integrated retrieval system, Entrez , which integrates data from the major DNA and protein sequence databases along with taxonomy, genome and protein structure information. MEDLINE(R) abstracts from published articles describing the sequences are also included as an additional source of biological annotation. Sequence similarity searching is offered through the BLAST series of database search programs. In addition to FTP, e-mail and server/client versions of Entrez and BLAST, NCBI offers a wide range of World Wide Web retrieval and analysis services of interest to biologists.

The Signal Recognition Particle Database (SRPDB)

This release of the SRPDB (signal recognition particle database, http://pegasus.uthct.edu/SRPDB/SRPDB . html ) adds four SRP RNA sequences (a total of 99 SRP RNA sequences), 23 SRP protein sequences (a total of 63 protein sequences from SRP9, SRP14, SRP19, SRP21, SRP54, SRP68 or SRP72), and, for the first time, sequences of the alpha subunit of the eukaryotic SRP receptor and its homologous bacterial proteins (a total of 21 sequences). Sequences are offered phylogenetically ordered, annotated with links to the primary databases, and in aligned form. Also downloadable are sample SRP RNA secondary structure diagrams, three-dimensional models of representative SRP RNAs, and search motifs.

Superior performance in protein homology detection with the Blocks Database servers

The Blocks Database World Wide Web (http://www.blocks.fhcrc.org ) and Email (blocks@blocks.fhcrc.org) servers provide tools for the detection and analysis of protein homology based on alignment blocks representing conserved regions of proteins. During the past year, searching has been augmented by supplementation of the Blocks Database with blocks from the Prints Database, for a total of 4754 blocks from 1163 families. Blocks from both the Blocks and Prints Databases and blocks that are constructed from sequences submitted to Block Maker can be used for blocks-versus-blocks searching of these databases with LAMA, and for viewing logos and bootstrap trees. Sensitive searches of up-to-date protein sequence databanks are carried out via direct links to the MAST server using position-specific scoring matrices and to the BLAST and PSI-BLAST servers using consensus-embedded sequence queries. Utilizing the trypsin family to evaluate performance, we illustrate the superiority of blocks-based tools over expert pairwise searching or Hidden Markov Models.

The tmRNA Website

tmRNA (also known as 10Sa RNA) is so-named for its dual tRNA-like and mRNA-like nature. It is employed in a remarkable trans -translation process to add a C-terminal peptide tag to the incomplete protein product of a broken mRNA; the tag targets the abnormal protein for proteolysis. tmRNA sequences have been identified in genomes of diverse bacterial phyla, including the most deeply branching. They have also been identified in plastids of the 'red' lineage. The tmRNA Website (http://www.wi.mit. edu/bartel/tmRNA/home ) contains a database currently including sequences from 37 species, with provisional alignments, as well as the tentatively predicted proteolysis tag sequences. A brief review and guide to the literature is also provided.

Histone Sequence Database: new histone fold family members

Searches of the major public protein databases with core and linker chicken and human histone sequences have resulted in the compilation of an annotated set of histone protein sequences. In addition, new database searches with two distinct motif search algorithms have identified several members of the histone fold family, including human DRAP1 and yeast CSE4. Database resources include information on conflicts between similar sequence entries in different source databases, multiple sequence alignments, links to the Entrez integrated information retrieval system, structures for histone and histone fold proteins, and the ability to visualize structural data through Cn3D. The database currently contains >1000 protein sequences, which are searchable by protein type, accession number, organism name, or any other free text appearing in the definition line of the entry. All sequences and alignments in this database are available through the World Wide Web at http://www.nhgri.nih. gov/DIR/GTB/HISTONES or http://www.ncbi.nlm.nih. gov/Baxevani/HISTONES

The Genome Sequence DataBase (GSDB): improving data quality and data access

In 1997 the primary focus of the Genome Sequence DataBase (GSDB; www. ncgr.org/gsdb ) located at the National Center for Genome Resources was to improve data quality and accessibility. Efforts to increase the quality of data within the database included two major projects; one to identify and remove all vector contamination from sequences in the database and one to create premier sequence sets (including both alignments and discontiguous sequences). Data accessibility was improved during the course of the last year in several ways. First, a graphical database sequence viewer was made available to researchers. Second, an update process was implemented for the web-based query tool, Maestro. Third, a web-based tool, Excerpt, was developed to retrieve selected regions of any sequence in the database. And lastly, a GSDB flatfile that contains annotation unique to GSDB (e.g., sequence analysis and alignment data) was developed. Additionally, the GSDB web site provides a tool for the detection of matrix attachment regions (MARs), which can be used to identify regions of high coding potential. The ultimate goal of this work is to make GSDB a more useful resource for genomic comparison studies and gene level studies by improving data quality and by providing data access capabilities that are consistent with the needs of both types of studies.

The ProDom database of protein domain families

The ProDom database contains protein domain families generated from the SWISS-PROT database by automated sequence comparisons. It can be searched on the World Wide Web (http://protein.toulouse.inra. fr/prodom.html ) or by E-mail (prodom@toulouse.inra.fr) to study domain arrangements within known families or new proteins. Strong emphasis has been put on the graphical user interface which allows for interactive analysis of protein homology relationships. Recent improvements to the server include: ProDom search by keyword; links to PROSITE and PDB entries; more sensitive ProDom similarity search with BLAST or WU-BLAST; alignments of query sequences with homologous ProDom domain families; and links to the SWISS-MODEL server (http: //www.expasy.ch/swissmod/SWISS-MODEL.html ) for homology based 3-D domain modelling where possible.

Archaeal-type lysyl-tRNA synthetase in the Lyme disease spirochete Borrelia burgdorferi

Lysyl-tRNAs are essential for protein biosynthesis by ribosomal mRNA translation in all organisms. They are synthesized by lysyl-tRNA synthetases (EC 6.1.1.6), a group of enzymes composed of two unrelated families. In bacteria and eukarya, all known lysyl-tRNA synthetases are subclass IIc-type aminoacyl-tRNA synthetases, whereas some archaea have been shown to contain an unrelated class I-type lysyl-tRNA synthetase. Examination of the preliminary genomic sequence of the bacterial pathogen Borrelia burgdorferi, the causative agent of Lyme disease, indicated the presence of an open reading frame with over 55% similarity at the amino acid level to archaeal class I-type lysyl-tRNA synthetases. In contrast, no coding region with significant similarity to any class II-type lysyl-tRNA synthetase could be detected. Heterologous expression of this open reading frame in Escherichia coli led to the production of a protein with canonical lysyl-tRNA synthetase activity in vitro. Analysis of B. burgdorferi mRNA showed that the lysyl-tRNA synthetase-encoding gene is highly expressed, confirming that B. burgdorferi contains a functional class I-type lysyl-tRNA synthetase. The detection of an archaeal-type lysyl-tRNA synthetase in B. burgdorferi and other pathogenic spirochetes, but not to date elsewhere in bacteria or eukarya, indicates that the gene that encodes this enzyme has a common origin with its orthologue from the archaeal kingdom. This difference between the lysyl-tRNA synthetases of spirochetes and their hosts may be readily exploitable for the development of anti-spirochete therapeutics.

Apparent mtDNA heteroplasmy in Alzheimer's disease patients and in normals due to PCR amplification of nucleus-embedded mtDNA pseudogenes

In an unprecedented finding, Davis et al. [Davis, R. E., Miller, S., Herrnstadt, C., Ghosh, S. S., Fahy, E., Shinobu, L. A., Galasko, D., Thal, L. J., Beal, M. F., Howell, N. & Parker, W. D., Jr. (1997) Proc. Natl. Acad. Sci. USA 94, 4526-4531] used an unusual DNA isolation method to show that healthy adults harbor a specific population of mutated mitochondrial cytochrome c oxidase (COX) genes that coexist with normal mtDNAs. They reported that this heteroplasmic population was present at a level of 10-15% in the blood of normal individuals and at a significantly higher level (20-30%) in patients with sporadic Alzheimer's disease. We provide compelling evidence that the DNA isolation method employed resulted in the coamplification of authentic mtDNA-encoded COX genes together with highly similar COX-like sequences embedded in nuclear DNA ("mtDNA pseudogenes"). We conclude that the observed heteroplasmy is an artifact.

Arabidopsis NPH1: a protein kinase with a putative redox-sensing domain

The NPH1 (nonphototropic hypocotyl 1) gene encodes an essential component acting very early in the signal-transduction chain for phototropism. Arabidopsis NPH1 contains a serine-threonine kinase domain and LOV1 and LOV2 repeats that share similarity (36 to 56 percent) with Halobacterium salinarium Bat, Azotobacter vinelandii NIFL, Neurospora crassa White Collar-1, Escherichia coli Aer, and the Eag family of potassium-channel proteins from Drosophila and mammals. Sequence similarity with a known (NIFL) and a suspected (Aer) flavoprotein suggests that NPH1 LOV1 and LOV2 may be flavin-binding domains that regulate kinase activity in response to blue light-induced redox changes.

Purification, cDNA cloning, and gene mapping of the small subunit of human DNA polymerase epsilon

HeLa DNA polymerase epsilon (pol epsilon), possibly involved in both DNA replication and DNA repair, consists of a catalytic subunit of 261 kDa and a tightly bound peptide with a relative molecular mass of 55 kDa. The cDNA of the 261-kDa polypeptide has been independently cloned, sequenced, and then overexpressed in insect cells to give a soluble, but catalytically unstable protein, suggesting that the small subunit of HeLa pol epsilon might be important for stability. HeLa pol epsilon has been isolated by immunoaffinity purification to obtain sequence information which enabled the cloning of a full-length human cDNA encoding the small subunit. The clone encoded nine proteolytic peptides obtained from the subunit. The 59,434-Da predicated polypeptide has 26% identity and 44% homology to the yeast pol epsilon 80-kDa subunit, DPB2. Using fluorescence in situ hybridization, the human pol epsilon p59 locus (DPE2) was assigned to chromosome 14q13-q21.

Bioinformatics: from genome data to biological knowledge

Recently, molecular biologists have sequenced about a dozen bacterial genomes and the first eukaryotic genome. We can now obtain answers to detailed questions about the complete set of genes of an organism. Bioinformatics methods are increasingly used for attaching biological knowledge to long lists of genes, assigning genes to biological pathways, comparing the gene sets of different species, identifying specificity factors, and describing sets of highly conserved proteins common to all domains of life. Substantial progress has recently been made in the availability of primary and added-value databases, in the development of algorithms and of network information services for genome analysis. The pharmaceutical industry has greatly benefited from the accumulation of sequence data through the identification of targets and candidates for the development of drugs, vaccines, diagnostic markers and therapeutic proteins.

Prokaryotic genomes: the emerging paradigm of genome-based microbiology

Comparative analysis of the complete sequences of seven bacterial and three archaeal genomes leads to the first generalizations of emerging genome-based microbiology. Protein sequences are, generally, highly conserved, with -70% of the gene products in bacteria and archaea containing ancient conserved regions. In contrast, there is little conservation of genome organization, except for a few essential operons. The most striking conclusions derived by comparison of multiple genomes from phylogenetically distant species are that the number of universally conserved gene families is very small and that multiple events of horizontal gene transfer and genome fusion are major forces in evolution.

Pendred syndrome is caused by mutations in a putative sulphate transporter gene (PDS)

Pendred syndrome is a recessively inherited disorder with the hallmark features of congenital deafness and thyroid goitre. By some estimates, the disorder may account for upwards of 10% of hereditary deafness. Previous genetic linkage studies localized the gene to a broad interval on human chromosome 7q22-31.1. Using a positional cloning strategy, we have identified the gene (PDS) mutated in Pendred syndrome and found three apparently deleterious mutations, each segregating with the disease in the respective families in which they occur. PDS produces a transcript of approximately 5 kb that was found to be expressed at significant levels only in the thyroid. The predicted protein, pendrin, is closely related to a number of known sulphate transporters. These studies provide compelling evidence that defects in pendrin cause Pendred syndrome thereby launching a new area of investigation into thyroid physiology, the pathogenesis of congenital deafness and the role of altered sulphate transport in human disease.

A diverse superfamily of enzymes with ATP-dependent carboxylate-amine/thiol ligase activity

The recently developed PSI-BLAST method for sequence database search and methods for motif analysis were used to define and expand a superfamily of enzymes with an unusual nucleotide-binding fold, referred to as palmate, or ATP-grasp fold. In addition to D-alanine-D-alanine ligase, glutathione synthetase, biotin carboxylase, and carbamoyl phosphate synthetase, enzymes with known three-dimensional structures, the ATP-grasp domain is predicted in the ribosomal protein S6 modification enzyme (RimK), urea amidolyase, tubulin-tyrosine ligase, and three enzymes of purine biosynthesis. All these enzymes possess ATP-dependent carboxylate-amine ligase activity, and their catalytic mechanisms are likely to include acylphosphate intermediates. The ATP-grasp superfamily also includes succinate-CoA ligase (both ADP-forming and GDP-forming variants), malate-CoA ligase, and ATP-citrate lyase, enzymes with a carboxylate-thiol ligase activity, and several uncharacterized proteins. These findings significantly extend the variety of the substrates of ATP-grasp enzymes and the range of biochemical pathways in which they are involved, and demonstrate the complementarity between structural comparison and powerful methods for sequence analysis.

A genomic perspective on protein families

In order to extract the maximum amount of information from the rapidly accumulating genome sequences, all conserved genes need to be classified according to their homologous relationships. Comparison of proteins encoded in seven complete genomes from five major phylogenetic lineages and elucidation of consistent patterns of sequence similarities allowed the delineation of 720 clusters of orthologous groups (COGs). Each COG consists of individual orthologous proteins or orthologous sets of paralogs from at least three lineages. Orthologs typically have the same function, allowing transfer of functional information from one member to an entire COG. This relation automatically yields a number of functional predictions for poorly characterized genomes. The COGs comprise a framework for functional and evolutionary genome analysis.

Crystal structure of a Hedgehog autoprocessing domain: homology between Hedgehog and self-splicing proteins

The approximately 25 kDa carboxy-terminal domain of Drosophila Hedgehog protein (Hh-C) possesses an autoprocessing activity that results in an intramolecular cleavage of full-length Hedgehog protein and covalent attachment of a cholesterol moiety to the newly generated amino-terminal fragment. We have identified a 17 kDa fragment of Hh-C (Hh-C17) active in the initiation of autoprocessing and report here its crystal structure. The Hh-C17 structure comprises two homologous subdomains that appear to have arisen from tandem duplication of a primordial gene. Residues in the Hh-C17 active site have been identified, and their role in Hedgehog autoprocessing probed by site-directed mutagenesis. Aspects of sequence, structure, and reaction mechanism are conserved between Hh-C17 and the self-splicing regions of inteins, permitting reconstruction of a plausible evolutionary history of Hh-C and the inteins.