3,326 research outputs found
Graph theoretic methods for the analysis of structural relationships in biological macromolecules
Subgraph isomorphism and maximum common subgraph isomorphism algorithms from graph theory provide an effective and an efficient way of identifying structural relationships between biological macromolecules. They thus provide a natural complement to the pattern matching algorithms that are used in bioinformatics to identify sequence relationships. Examples are provided of the use of graph theory to analyze proteins for which three-dimensional crystallographic or NMR structures are available, focusing on the use of the Bron-Kerbosch clique detection algorithm to identify common folding motifs and of the Ullmann subgraph isomorphism algorithm to identify patterns of amino acid residues. Our methods are also applicable to other types of biological macromolecule, such as carbohydrate and nucleic acid structures
Probing the limits to microRNA-mediated control of gene expression
According to the `ceRNA hypothesis', microRNAs (miRNAs) may act as mediators
of an effective positive interaction between long coding or non-coding RNA
molecules, carrying significant potential implications for a variety of
biological processes. Here, inspired by recent work providing a quantitative
description of small regulatory elements as information-conveying channels, we
characterize the effectiveness of miRNA-mediated regulation in terms of the
optimal information flow achievable between modulator (transcription factors)
and target nodes (long RNAs). Our findings show that, while a sufficiently
large degree of target derepression is needed to activate miRNA-mediated
transmission, (a) in case of differential mechanisms of complex processing
and/or transcriptional capabilities, regulation by a post-transcriptional
miRNA-channel can outperform that achieved through direct transcriptional
control; moreover, (b) in the presence of large populations of weakly
interacting miRNA molecules the extra noise coming from titration disappears,
allowing the miRNA-channel to process information as effectively as the direct
channel. These observations establish the limits of miRNA-mediated
post-transcriptional cross-talk and suggest that, besides providing a degree of
noise buffering, this type of control may be effectively employed in cells both
as a failsafe mechanism and as a preferential fine tuner of gene expression,
pointing to the specific situations in which each of these functionalities is
maximized.Comment: 16 page
Elucidation of Directionality for Co-Expressed Genes: Predicting Intra-Operon Termination Sites
We present a novel framework for inferring regulatory and sequence-level
information from gene co-expression networks. The key idea of our methodology
is the systematic integration of network inference and network topological
analysis approaches for uncovering biological insights. We determine the gene
co-expression network of Bacillus subtilis using Affymetrix GeneChip time
series data and show how the inferred network topology can be linked to
sequence-level information hard-wired in the organism's genome. We propose a
systematic way for determining the correlation threshold at which two genes are
assessed to be co-expressed by using the clustering coefficient and we expand
the scope of the gene co-expression network by proposing the slope ratio metric
as a means for incorporating directionality on the edges. We show through
specific examples for B. subtilis that by incorporating expression level
information in addition to the temporal expression patterns, we can uncover
sequence-level biological insights. In particular, we are able to identify a
number of cases where (i) the co-expressed genes are part of a single
transcriptional unit or operon and (ii) the inferred directionality arises due
to the presence of intra-operon transcription termination sites.Comment: 7 pages, 8 figures, accepted in Bioinformatic
The use of information theory in evolutionary biology
Information is a key concept in evolutionary biology. Information is stored
in biological organism's genomes, and used to generate the organism as well as
to maintain and control it. Information is also "that which evolves". When a
population adapts to a local environment, information about this environment is
fixed in a representative genome. However, when an environment changes,
information can be lost. At the same time, information is processed by animal
brains to survive in complex environments, and the capacity for information
processing also evolves. Here I review applications of information theory to
the evolution of proteins as well as to the evolution of information processing
in simulated agents that adapt to perform a complex task.Comment: 25 pages, 7 figures. To appear in "The Year in Evolutionary Biology",
of the Annals of the NY Academy of Science
Classes of fast and specific search mechanisms for proteins on DNA
Problems of search and recognition appear over different scales in biological
systems. In this review we focus on the challenges posed by interactions
between proteins, in particular transcription factors, and DNA and possible
mechanisms which allow for a fast and selective target location. Initially we
argue that DNA-binding proteins can be classified, broadly, into three distinct
classes which we illustrate using experimental data. Each class calls for a
different search process and we discuss the possible application of different
search mechanisms proposed over the years to each class. The main thrust of
this review is a new mechanism which is based on barrier discrimination. We
introduce the model and analyze in detail its consequences. It is shown that
this mechanism applies to all classes of transcription factors and can lead to
a fast and specific search. Moreover, it is shown that the mechanism has
interesting transient features which allow for stability at the target despite
rapid binding and unbinding of the transcription factor from the target.Comment: 65 pages, 23 figure
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