Biomedical subjects

S A Shabalina

Publications and source records attributed to S A Shabalina.

16 recordsLinked to original sources

PubMed2006

Human catechol-O-methyltransferase haplotypes modulate protein expression by altering mRNA secondary structure.

Catechol-O-methyltransferase (COMT) is a key regulator of pain perception, cognitive function, and affective mood. Three common haplotypes of the human COMT gene, divergent in two synonymous and one nonsynonymous position, code for differences in COMT enzymatic activity and are associated with pain sensitivity. Haplotypes divergent in synonymous changes exhibited the largest difference in COMT enzymatic activity, due to a reduced amount of translated protein. The major COMT haplotypes varied with respect to messenger RNA local stem-loop structures, such that the most stable structure was associated with the lowest protein levels and enzymatic activity. Site-directed mutagenesis that eliminated the stable structure restored the amount of translated protein. These data highlight the functional significance of synonymous variations and suggest the importance of haplotypes over single-nucleotide polymorphisms for analysis of genetic variations.

Alleles↗

PubMed2003

Thermodynamic criteria for high hit rate antisense oligonucleotide design.

Antisense oligonucleotides are used for therapeutic applications and in functional genomic studies. In practice, however, many of the oligonucleotides complementary to an mRNA have little or no antisense activity. Theoretical strategies to improve the 'hit rate' in antisense screens will reduce the cost of discovery and may lead to identification of antisense oligonucleotides with increased potency. Statistical analysis performed on data collected from more than 1000 experiments with phosphorothioate-modified oligonucleotides revealed that the oligo-probes, which form stable duplexes with RNA (DeltaG(o)37 < or = -30 kcal/mol) and have small self-interaction potential, are more frequently efficient than molecules that form less stable oligonucleotide-RNA hybrids or more stable self-structures. To achieve optimal statistical preference, the values for self-interaction should be (DeltaG(o)37) > or = -8 kcal/mol for inter-oligonucleotide pairing and (DeltaG(o)37) > or = -1.1 kcal/mol for intra-molecular pairing. Selection of oligonucleotides with these thermodynamic values in the analyzed experiments would have increased the 'hit rate' by as much as 6-fold.

Chemistry, Pharmaceutical↗

PubMed2003

Thermodynamic calculations and statistical correlations for oligo-probes design.

Optimization of probe design for array-based experiments requires improved predictability of oligonucleotide hybridization behavior. Currently, designing oligonucleotides capable of interacting efficiently and specifically with the relevant target is not a routine procedure. Multiple examples demonstrate that oligonucleotides targeting different regions of the same RNA differ in their hybridization ability. The present work shows how thermodynamic evaluations of oligo-target duplex or oligo self-structure stabilities can facilitate probe design. Statistical analysis of large sets of hybridization data reveals that thermodynamic evaluation of oligonucleotide properties can be used to avoid poor RNA binders. Thermodynamic criteria for the selection of 20 and 21mers, which, with high probability, interact efficiently and specifically with their targets, are suggested. The design of longer oligonucleotides can also be facilitated by the same calculations of DeltaG(o) (T) values for oligo-target duplex or oligo self-structure stabilities and similar selection schemes.

Nucleic Acid Hybridization↗

PubMed2003

Conserved fragments of transposable elements in intergenic regions: evidence for widespread recruitment of MIR- and L2-derived sequences within the mouse and human genomes.

We analysed the distribution of transposable elements (TEs) in 100 aligned pairs of orthologous intergenic regions from the mouse and human genomes. Within these regions, conserved segments of high similarity between the two species alternate with segments of low similarity. Identifiable TEs comprise 40-60% of segments of low similarity. Within such segments, a particular copy of a TE found in one species has no orthologue in the other. Overall, TEs comprise only approximately 20 % of conserved segments. However, TEs from two families, MIR and L2, are rather common within conserved segments. Statistical analysis of the distributions of TEs suggests that a majority of the MIR and L2 elements present in murine intergenic regions have human orthologues. These elements must have been present in the common ancestor of human and mouse and have remained under substantial negative selection that prevented their divergence beyond recognition. If so, recruitment of MIR- and L2-derived sequences to perform a function that increases host fitness is rather common, with at least two such events per host gene. The central part of the MIR consensus sequence is over-represented in conserved segments given its background frequency in the genome, suggesting that it is under the strongest selective constraint.

Animals↗

PubMed2001

Selective constraint in intergenic regions of human and mouse genomes.

We aligned and analyzed 100 pairs of complete, orthologous intergenic regions from the human and mouse genomes (average length approximately 12 000 nucleotides). The alignments alternate between highly similar segments and dissimilar segments, indicating a wide variation of selective constraint. The average number of selectively constrained nucleotides within a mammalian intergenic region is at least 2000. This is threefold higher than within a nematode intergenic region and at least twofold higher than the number of selectively constrained nucleotides coding for an average protein. Because mammals possess only two- to threefold more proteins than Caenorhabditis elegans, the higher complexity of mammals might be primarily because of the functioning of intergenic DNA.

Animals↗

PubMed2000

Identification of sequence motifs in oligonucleotides whose presence is correlated with antisense activity.

Design of antisense oligonucleotides targeting any mRNA can be much more efficient when several activity-enhancing motifs are included and activity-decreasing motifs are avoided. This conclusion was made after statistical analysis of data collected from >1000 experiments with phosphorothioate-modified oligonucleotides. Highly significant positive correlation between the presence of motifs CCAC, TCCC, ACTC, GCCA and CTCT in the oligonucleotide and its antisense efficiency was demonstrated. In addition, negative correlation was revealed for the motifs GGGG, ACTG, AAA and TAA. It was found that the likelihood of activity of an oligonucleotide against a desired mRNA target is sequence motif content dependent.

Base Composition↗

PubMed1999

Pattern of selective constraint in C. elegans and C. briggsae genomes.

Similarity between related genomes may carry information on selective constraint in each of them. We analysed patterns of similarity between several homologous regions of Caenorhabditis elegans and C. briggsae genomes. All homologous exons are quite similar. Alignments of introns and of intergenic sequences contain long gaps, segments where similarity is low and close to that between random sequences aligned using the same parameters, and segments of high similarity. Conservative estimates of the fractions of selectively constrained nucleotides are 72%, 17% and 18% for exons, introns and intergenic sequences, respectively. This implies that the total number of constrained nucleotides within non-coding sequences is comparable to that within coding sequences, so that at least one-third of nucleotides in C. elegans and C. briggsae genomes are under strong stabilizing selection.

Animals↗

PubMed1997

Rapid decline of fitness in panmictic populations of Drosophila melanogaster maintained under relaxed natural selection.

The parameters of the spontaneous deleterious mutation process remain poorly known, despite their importance. Here, we report the results of a mutation accumulation experiment performed on panmictic populations of Drosophila melanogaster without any genetic manipulations. Two experimental populations were kept for 30 generations under relaxed natural selection. Each generation, 100 pairs were formed randomly, and every fecund pair contributed a son and a daughter to the next generation. Comparison with two controls, one cryopreserved and the other kept as the experimental populations but with long generation time, showed that the number of surviving offspring per female declined by 0.2% and 2.0% per generation under benign and harsh, competitive conditions, respectively. Thus, the mutational pressure on fitness may be strong and depends critically on the conditions under which fitness is assayed.

Animals↗

PubMed1995

SAMSON: a software package for the biopolymer primary structure analysis.

The SAMSON package is a tool for advanced analysis of primary DNA, RNA and protein structures. The package consists of 16 programs performing statistical analysis and comparison of biopolymer sequences, search for homologies, translation of DNA and RNA sequences into amino acid sequences, splicing of RNA sequences and restriction map construction, recognition of functionally related sites in biopolymer molecules, textual analysis of DNA and RNA regulatory sites and prediction of intermolecular hybridization sites in DNA and RNA molecules.

Algorithms↗

PubMed1993

Calculation of contributions of individual monomeric units to biopolymer function.

The possibility of determination of individual monomeric unit contributions into biopolymer function based on the data on biopolymer primary structures and functional activities is discussed. We show that even the most complete set of data do not allow to determine the absolute contributions of monomeric units, while their relative contributions may be determined.

Animals↗

PubMed1993

Intermolecular mRNA-rRNA hybridization and the distribution of potential interaction regions in murine 18S rRNA.

Intermolecular hybridization experiments show that murine 18S rRNA and 28S rRNA are capable of forming stable hybrid structures with mRNA from genes p53, c-myc and c-mos from the same species. Both 5'-uncoding and coding oncogene p53 mRNA regions contain fragments interacting with rRNA. Computer analysis revealed 18S rRNA fragments complementary to oligonucleotides frequently met in mRNA, which are potential hybridization regions (clinger-fragments). The distribution of clinger-fragments along 18S rRNA sequence is universal at least for one hundred murine mRNA sequences analyzed. Maximal frequencies of oligonucleotides complementary to 18S rRNA clinger-fragments are reliably (2-3 times) higher for mRNA than for intron sequences and randomly generated sequences. The results obtained suggest a possible role of clinger-fragments in translation processes as universal regions of mRNA binding.

Animals↗

PubMed1992

Effect of Galleria mellonella larvae preparation and honeybee products on cell cultures.

1. The action of the extract from larvae of the great wax moth Galleria mellonella L. used in Russian folk medicine was studied. 2. Two active components influencing the growth and morphological differentiation of cells in vitro were found. 3. The presence of these components in the extract was conditioned by consumption of honeybee products by Galleria mellonella larvae. 4. Cytotoxicity of honeybee products was studied.

Animals↗

PubMed1991

On the frequencies of nucleotides and nucleotide substitutions in conservative regulatory DNA sequences.

We present data on the frequencies of nucleotides and nucleotide substitutions in conservative DNA regions involved in the regulation of gene expression. Data on prokaryotes and eukaryotes are considered separately. In both cases DNA strands complementary to those which serve as templates for RNA-polymerase have low frequencies of cytosine. The most conservative positions also have an increased frequency of adenine. Various substitutions in the series of homologous regulatory DNA sequences, as compared to their consensuses, have different frequencies. In prokaryotes guanine in a consensus sequence is substituted for at the lowest and adenine at the highest frequency, whereas in eukaryotes cytosine is substituted for at the lowest and guanine at the highest frequency. In both cases the nucleotides substituted for are most frequently replaced with cytosine. Deviations from consensus sequences tend to cluster in adjacent positions. The more pronounced the consequences of a nucleotide substitution are the higher is the frequency of substitutions in adjacent positions. Possible explanations for these phenomena are discussed.

Animals↗

PubMedDate not supplied

[Region of intermolecular complementarity in Escherichia coli 16S rRNA, mRNA, and tRNA molecules].

The results of computer analysis of complementarity regions in the sequences of E. coli 16S rRNA, mRNAs and tRNAs are reported in this article. The potential regions of intermolecular RNA-RNA hybridization, or clinger fragments, in 16S rRNA, which are complementary to the sites frequently occurring in mRNAs and tRNAs, were found. Major clinger fragments on 16S rRNA are universal for genes that belong to different functional groups. Our results show there are adaptations of the structural organization of the 16S rRNA molecule to messenger and transport RNA sequences. RNA interaction with clinger fragments may contribute to upregulation of translation process through increasing the local concentration of mRNAs and tRNAs in the vicinity of the ribosome and their proper positioning, as well as decrease the efficiency of translation through non-specific mRNA-16SrRNA interactions.

Escherichia coli↗

PubMedDate not supplied

[The computer program package "SAMSON" for analysis of primary structure of biopolymers].

A program package "SAMSON" for the computer analysis of biopolymer primary structures is described. All possible modes of sequence investigation are considered. The programs for sequence comparison are described in some details. The general principles of a program package organisation and of its user interface are also mentioned. For more complete information see Vernoslov S.E. et al. "Program package "SAMSON" for the analysis of the polymer primary structures", parts 1 and 2, Poustchino, ONTI NCBI, 1989.

Base Sequence↗

PubMedDate not supplied

[A model of multiple contacts, describing the interaction of rRNA sites with mRNA].

A model describing the interaction of a short oligonucleotide with long polynucleotide matrix has been developed. The model allows to calculate possibilities of oligonucleotide binding with different matrix sites on the basis of thermodynamic parameters of duplex formation. The model has been used for description of messenger RNA interaction with "clinger-fragment" sites on ribosomal RNA, which are potential sites of hybridization with mRNA. A possibility of rRNA interaction with mRNA by means of multiple duplex formation between "clinger-fragments" and numerous complementary short mRNA sites is discussed.

Base Sequence↗