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Biomedical subjects

T G Marr

Publications and source records attributed to T G Marr.

12 recordsLinked to original sources
PubMed1996

Complementary classification approaches for protein sequences.

We have studied five methods of protein classification and have applied them to the 768 groups of related proteins in the PROSITE catalog. Four of these methods are based on searching a database of blocks, and the other uses the frequently occurring motifs found in the protein families combined with a fingerprint technique. Our experimental results show that the block-based methods perform well when taking into account the probability of amino acids occurring in a block. Furthermore, the five methods give information that is complementary to each other. Thus, using the five methods together, one can obtain high confidence classifications (if the results agree) or suggest alternative hypotheses (if the results disagree). We also list those proteins whose current families documented in the PROSITE catalog differ from those suggested by our results. There are remarkably few of them, which is a testimony to the quality of PROSITE.

Amino Acid Sequence↗
PubMed1995

Alignment of molecular sequences seen as random path analysis.

We propose a generating functional method--random path analysis (RPA)--that generalizes the classical dynamic programming (DP) method widely used in sequence alignments. For a given cost function, DP is a deterministic method that finds an optimal alignment by minimizing the total cost function for all possible alignments. By allowing uncertainty, RPA is a statistical method that weights fluctuating alignments by probabilities. Therefore, DP maybe thought of as the deterministic limit of RPA when the fluctuations approach zero. DP is the method of choice if one is only interested in optimal alignment. But we argue that, when information beyond the optimal alignment is desired, RPA gives a natural extension of DP for biological applications. As an algebraic approach, RPA is computationally intensive for long sequences, but it can provide better parametric control for developing analytical or perturbational results and it is more informative and biologically relevant. The idea of RPA opens up new opportunities for simulational approaches and more importantly it suggests a novel hardware implementation that has the potential of improving the way a sequence alignment is done. Here we focus on deriving a mathematically rigorous solution to RPA both in its combinatorial form and in its graphical representation; this puts DP in logical perspective under a more general conceptual framework.

Animals↗
PubMed1995

Evidence for linkage of bipolar disorder to chromosome 18 with a parent-of-origin effect.

A susceptibility gene on chromosome 18 and a parent-of-origin effect have been suggested for bipolar affective disorder (BPAD). We have studied 28 nuclear families selected for apparent unilineal transmission of the BPAD phenotype, by using 31 polymorphic markers spanning chromosome 18. Evidence for linkage was tested with affected-sib-pair and LOD score methods under two definitions of the affected phenotype. The affected-sibpair analyses indicated excess allele sharing for markers on 18p within the region reported previously. The greatest sharing was at D18S37: 64% in bipolar and recurrent unipolar (RUP) sib pairs (P = .0006). In addition, excess sharing of the paternally, but not maternally, transmitted alleles was observed at three markers on 18q: at D18S41, 51 bipolar and RUP sib pairs were concordant for paternally transmitted alleles, and 21 pairs were discordant (P = 0004). The evidence for linkage to loci on both 18p and 18q was strongest in the 11 paternal pedigrees, i.e., those in which the father or one of the father's sibs is affected. In these pedigrees, the greatest allele sharing (81%; P = .00002) and the highest LOD score (3.51; phi = 0.0) were observed at D18S41. Our results provide further support for linkage of BPAD to chromosome 18 and the first molecular evidence for a parent-of-origin effect operating in this disorder. The number of loci involved, and their precise location, require further study..

Adolescent↗
PubMed1994

Discovering active motifs in sets of related protein sequences and using them for classification.

We describe a method for discovering active motifs in a set of related protein sequences. The method is an automatic two step process: (1) find candidate motifs in a small sample of the sequences; (2) test whether these motifs are approximately present in all the sequences. To reduce the running time, we develop two optimization heuristics based on statistical estimation and pattern matching techniques. Experimental results obtained by running these algorithms on generated data and functionally related proteins demonstrate the good performance of the presented method compared with visual method of O'Farrell and Leopold. By combining the discovered motifs with an existing fingerprint technique, we develop a protein classifier. When we apply the classifier to the 698 groups of related proteins in the PROSITE catalog, it gives information that is complementary to the BLOCKS protein classifier of Henikoff and Henikoff. Thus, using our classifier in conjunction with theirs, one can obtain high confidence classifications (if BLOCKS and our classifier agree) or suggest a new hypothesis (if the two disagree).

Algorithms↗
PubMed1994

A sequence compilation and comparison of exons that are alternatively spliced in neurons.

Alternative splicing is an important regulatory mechanism to create protein diversity. In order to elucidate possible regulatory elements common to neuron specific exons, we created and statistically analysed a database of exons that are alternatively spliced in neurons. The splice site comparison of alternatively and constitutively spliced exons reveals that some, but not all alternatively spliced exons have splice sites deviating from the consensus sequence, implying diverse patterns of regulation. The deviation from the consensus is most evident at the -3 position of the 3' splice site and the +4 and -3 position of the 5' splice site. The nucleotide composition of alternatively and constitutively spliced exons is different, with alternatively spliced exons being more AU rich. We performed overlapping k-tuple analysis to identify common motifs. We found that alternatively and constitutively spliced exons differ in the frequency of several trinucleotides that cannot be explained by the amino acid composition and may be important for splicing regulation.

Alternative Splicing↗
PubMed1994

Fission yeast gene structure and recognition.

A database of 210 Schizosaccharomyces pombe DNA sequences (524,794 bp) was extracted from GenBank (release number 81.0) and examined by a number of methods in order to characterize statistical features of these sequences that might serve as signals or constraints for messenger RNA splicing. The statistical information compiled includes splicing signal (donor, acceptor and branch site) profiles, translational initiation start profile, exon/intron length distributions, ORF distribution, CDS size distribution, codon usage table, and 6-tuple distribution. The information content of the various signals are also presented. A rule-based interactive computer program for finding introns called INTRON.PLOT has been developed and was used to successfully analyze 7 newly sequenced genes.

Base Sequence↗
PubMed1993

A 13 kb resolution cosmid map of the 14 Mb fission yeast genome by nonrandom sequence-tagged site mapping.

We present the application of a nonrandom sequence-tagged site (STS) content detection method in mapping an entire genome, that of fission yeast. The novelty of our strategy is in the use of STS probes made from both ends of cosmid clones, selected on the basis of "sample without replacement" (only library clones that show no previous positive hybridization are selected and made into probes). We developed powerful techniques, based on consistency analysis, for error detection and contig assembly. In addition, we probed our library with genetically mapped markers and Notl or Sfil linking clones, thereby anchoring contigs onto chromosomes. Our map contains more than 1000 sites, including genes (most were previously unmapped), occurrences of known repetitive elements, and Notl-Sfil restriction sites.

Chromosome Mapping↗
PubMed1993

Genome mapping by nonrandom anchoring: a discrete theoretical analysis.

As part of our effort to construct a physical map of the genome of the fission yeast Schizosaccharomyces pombe, we have made theoretical predictions for the progress expected, as measured by the expected length fraction of island coverage and by the expected properties of the anchored islands such as the number and the size of islands. Our experimental strategy is to construct a random clone library and screen the library for clones having unique sequence at both ends. This scheme is essentially the same as the clone-limited double sequence-tagged-site selection scheme which was used in a computer simulation by Palazzolo et al. [Palazzolo, M. J., Sawyer, S. A., Martin, C. H., Smoller, D. A. & Hartl, D. L. (1991) Proc. Natl. Acad. Sci. USA 88, 8034-8038]. Both simulation and ongoing experiments in our laboratory have shown that the nonrandom anchoring method is far superior to random anchoring. In this paper, we propose a theoretical model to explain the simulated data and the experimental data.

Chromosome Mapping↗
PubMed1993

A weight array method for splicing signal analysis.

A new method of sequence analysis, using a weight array method (WAM), which generalizes the traditional Staden weight matrix method (WMM), is proposed. With the help of a statistical mechanical model, the discriminant function is identified with the energy function describing macromolecular interactions. The method is applied to the study of 5'-splice signals in Schizosaccharomyces pombe pre-mRNA sequences. The results show that there may exist weak pairwise correlations within the signals and that our method can help to better discriminate these signals. Experiments are proposed to test the predictions of the theory.

Animals↗
PubMed1992

Genomic mapping by single copy landmark detection: a predictive model with a discrete mathematical approach.

One of the goals of the Human Genome Project is to produce libraries of largely contiguous, ordered sets of molecular clones for use in sequencing and gene mapping projects. This is planned to be done for human and many model organisms. Theory and practice have shown that long-range contiguity and the degree to which the entire genome is covered by ordered clones can be affected by many biological variables. Many laboratories are currently experimenting with different experimental strategies and theoretical models to help plan strategies for accomplishing long-range molecular mapping of genomes. Here we describe a new mathematical model and formulas for helping to plan genome mapping projects, using various single-copy landmark (SCL) detection, or "anchoring", strategies. We derive formulas that allow us to examine the effects of interactions among the following variables: average insert size of the cloning vector, average size of SCL, the number of SCL, and the redundancy in coverage of the clone library. We also examine and compare three different ways in which anchoring can be implemented: (1) anchors are selected independently of the library to be ordered (random anchoring); (2) anchors are made from end probes from both ends of clones in the library to be ordered (nonrandom anchoring); and (3) anchors are made from one end or the other, randomly, from clones in the library to be ordered (nonrandom anchoring). Our results show that, for biologically realistic conditions, nonrandom anchoring is always more effective than random anchoring for contig building, and there is little to be gained from making SCL from both ends of clones vs. only one end of clones.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromosome Mapping↗
PubMed1988

The need for national HIV databases.

Researchers and public health officials involved in surveying and forecasting the course of the HIV epidemic require complete and unfiltered information from many sources. Governments should respond by establishing national HIV databases.

Acquired Immunodeficiency Syndrome↗