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I Marín

Publications and source records attributed to I Marín.

33 records · Page 2Linked to original sources
PubMed1996

The dosage compensation system of Drosophila is co-opted by newly evolved X chromosomes.

In species where males and females differ in number of sex chromosomes, the expression of sex-linked genes is equalized by a process known as dosage compensation. In Drosophila melanogaster, dosage compensation is mediated by the binding of the products of the male-specific lethal (msl) genes to the single male X chromosome. Here we report that the sex- and chromosome-specific binding of three of the msl proteins (MSLs) occurs in other drosophilid species, spanning four genera. Moreover, we show that MSL binding correlates with the evolution of the sex chromosomes: in species that have acquired a second X chromosome arm because of an X-autosome translocation, we observe binding of the MSLs to the 'new' (previously autosomal) arm of the X chromosome, only when its homologue has degenerated. Moreover, in Drosophila miranda, a Y-autosome translocation has produced a new X chromosome (called neo-X), only some regions of which are dosage compensated. In this neo-X chromosome, the pattern of MSL binding correlates with the known pattern of dosage compensation.

Animals↗
PubMed1996

Evolutionary conservation and molecular characteristics of repetitive sequences of Drosophila koepferae.

Thirteen middle repetitive DNA clones obtained from the genome of Drosophila koepferae have been tested for their evolutionary conservation in the other seven species of the buzzatii and martensis clusters (repleta group). All but two of these clones exhibit qualitatively similar patterns of hybridization in the eight species. The average interspecific hybridization signal is 85 per cent of that found intraspecifically, ranging from 73 to 93 per cent. Partial sequencing of six of these clones has shown sequences related to the retrotransposon Gypsy, first characterized in D. melanogaster, as well as to the Anopheles gambiae LINE elements T1Ag and Q. A fragment of a hitherto unknown, short inverted repeat transposable element has also been found. The evolutionary conservation of repetitive D. koepferae sequences seems to be related to the high proportion of simple DNA and inactive mobile elements in the genome of this species.

Amino Acid Sequence↗
PubMed1996

Genetic architecture of autosome-mediated hybrid male sterility in Drosophila.

Several estimators have been developed for assessing the number of sterility factors in a chromosome based on the sizes of fertile and sterile introgressed fragments. Assuming that two factors are required for producing sterility, simulations show that one of these, twice the inverse of the relative size of the largest fertile fragment, provides good average approximations when as few as five fertile fragments are analyzed. The estimators have been used for deducing the number of factors from previous data on several pairs of species. A particular result contrasts with the authors' interpretations: instead of the high number of sterility factors suggested, only a few per autosome are estimated in both reciprocal crosses involving Drosophila buzzatii and D. koepferae. It has been possible to map these factors, between three and six per chromosome, in the autosomes 3 and 4 of these species. Out of 203 introgressions of different fragments or combinations of fragments, the outcome of at least 192 is explained by the mapped zones. These results suggest that autosome-mediated sterility in the male hybrids of these species is mediated by a few epistatic factors, similarly to X-mediated sterility in the hybrids of other Drosophila species.

Animals↗
PubMed1996

Restriction analysis of actinomycetes chromosomal DNA.

Actinomycetes DNAs were digested with restriction enzymes to study the presence of methylated bases. Analysis showed that the enterobacterial Dam and Dcm systems are absent. Methylation at the internal cytosine in CCGG sequences, typical of eukaryotes, was also absent. We also tested 18 restriction endonucleases recognizing six base pair sequences (all of which were inhibited by methylation). Results showed a higher number of restriction sites for enzymes recognizing CG-rich sequences (CG endonucleases) than for enzymes recognizing AT-rich sequences (AT endonucleases). Restriction patterns with CG endonucleases were quite uniform, with the remarkable exception of XhoI, which yielded a small number of DNA bands. The study performed with AT endonucleases allowed differentiation of three groups of enzymes based on different degrees of chromosomal sensitivity. One group (BclI and BglII) produced restriction patterns with more abundant restriction sites than expected, a second group (ClaI, EcoRI, and EcoRV) yielded the predicted number of DNA fragments, and the third group (HpaI, HindIII, XbaI, and DraI) produced an unexpectedly low number of fragments. Some individual cases of resistance to particular enzymes could be explained by the presence of restriction-modification systems with the same specificity.

Actinomycetales↗
PubMed1995

High-ionic strength interference of ribosomal inhibition produced by aminoglycoside antibiotics.

A protein synthesis cell-free system capable of performing with similar efficiencies in different ionic conditions has been developed for the halotolerant marine bacterium Vibrio costicola. The system has been used to test the effect of ionic strength on the interference produced by thirty translation inhibitors with different structural, functional, and domain specificities. In general, at high ionic strengths, the inhibition of protein synthesis produced by polycationic antibiotics like the aminoglycosides is much less pronounced than the inhibition obtained at low ionic strengths, while non-aminoglycosidic antibiotics show similar inhibitory activities at both high and low ionic conditions. These results strongly suggest that competition between polycationic antibiotics and cations at high concentrations in the media is responsible for the lack of inhibition by aminoglycoside antibiotics at high ionic strengths, rather than a lack of binding sites.

Aminoglycosides↗
PubMed1995

Characterization of Gandalf, a new inverted-repeat transposable element of Drosophila koepferae.

The cloning and characterization of Gandalf, a new DNA-transposing mobile element obtained from the Drosophila koepferae (repleta group) genome is described. A fragment of Gandalf was found in a middle repetitive clone that shows variable chromosomal localization. Restriction, Southern blot, PCR and sequencing analyses have shown that most Gandalf copies are about 1 kb long, are flanked by 12 bp inverted terminal repeats and contain subterminal repetitive regions on both sides of the element. As with other elements of the DNA-transposing type (known as the 'Ac family'), the Gandalf element generates 8 bp direct duplications at the insertion point. Coding region analysis has shown that the longer open reading frame found in Gandalf copies could encode part of a protein. However, whether or not the 1 kb copies of the element are actually the active transposons remains to be elucidated. Gandalf shows a very low copy number in D. buzzatii, a sibling species of D. koepferae. An attempt to induce interspecific hybrid dysgenesis in hybrids of these two species has been unsuccessful.

Animals↗
PubMed1989

The use of functional analysis of the ribosome as a tool to determine archaebacterial phylogeny.

Forty different antibiotics with diverse kingdom and functional specificities were used to measure the functional characteristics of the archaebacterial translation apparatus. The resulting inhibitory curves, which are characteristic of the cell-free system analyzed, were transformed into quantitative values that were used to cluster the different archaebacteria analyzed. This cluster resembles the phylogenetic tree generated by 16S rRNA sequence comparisons. These results strongly suggest that functional analysis of an appropriate evolutionary clock, such as the ribosome, is of intrinsic phylogenetic value. More importantly, they indicate that the study of the nexus between genotypic and phenotypic (functional) information may shed considerable light on the evolution of the protein synthetic machinery.

Archaea↗
PubMed1988

Variable rRNA gene copies in extreme halobacteria.

Using PFG electrophoresis techniques, we have examined the organization of rRNA gene in halobacterium species. The results show that the organization of rRNA genes among closely related halobacteria is quite heterogeneous. This contrasts with the high degree of conservation of rRNA sequence (1). The possible mechanism of such rRNA gene amplification and its evolutionary implications are discussed.

DNA, Bacterial↗
PubMedDate not supplied

Stable Drosophila buzzatii-Drosophila koepferae hybrids.

Previous experiments discovered high rates of chromosomal rearrangements in the progeny of males containing a telomeric segment of Drosophila koepferae in a D. buzzatii genetic background (segmental males). We have performed similar experiments, designed to test whether this chromosomal instability could be explained by a phenomenon similar to P-M hybrid dysgenesis or, alternatively, by a generalized telomeric effect. However, the results obtained have not allowed us to fully characterize this process, because we have not observed chromosomal rearrangements in the progeny of the putative unstable males. Our results suggest that chromosomal instability is independent of the introgressed fragment. A reasonable hypothesis to explain these results is that mutator factors are occasionally introduced by the hybridization. The effect of sampling, caused by the fact that only a small region is introgressed in a particular line, may explain why only some hybridizations lead to instability.

Animals↗
PubMedDate not supplied

[The efficacy of neurophysiological examination in the diagnosis of carpal tunnel syndrome].

INTRODUCTION: The validity of studies of nerve conduction in the diagnosis of carpal tunnel syndrome has been sufficiently demonstrated, especially the speed of nerve conduction across the carpus. It has also been proved that the result of the test varies according to its use. OBJECTIVE: This study is to evaluate the result of the study of nerve conduction in the diagnosis of carpal tunnel syndrome in a population attending a clinical neurophysiology department for examination of suspected neuro-muscular disorders of the upper limit. PATIENTS AND METHODS: We selected the cut-off points of the values of speed of nerve conduction along the median nerve from the thumb (E1) and palm of the hand (E2). Those showing the best sensitivity and specificity were chosen (53 and 51 m/s respectively). We assessed the pre-test and post-test probability to measure the examination result. There was little contribution from this examination to the diagnosis of carpal tunnel syndrome in this population. CONCLUSIONS: The high pre-test probability of a disorder is a cause of low efficacy of the examination done to confirm this and the opposite occurs when it is done to rule it out. The efficacy of an examination should be measured in the setting in which it is used since this does not depend only on its intrinsic characteristics but also on how it is used.

Adolescent↗
PubMedDate not supplied

Biocorrosion produced by Thiobacillus-like microorganisms.

Biocorrosion can be produced by many different microorganisms through diverse mechanisms. The biocorrosion produced by acidophilic microorganisms of the genus Thiobacillus is based on the production of sulfuric acid and ferric ion from pyrites or related mineral structures, as a result of the chemolithotrophic metabolism of these microorganisms. The products of this aerobic respiration are also powerful oxidant elements, which can produce chemical oxidations of other metallic structures. The Tinto River, a very unusual extremophilic habitat (pH around 2, and high concentration of ferric ion), product of the growth of strict chemolithotrophic microorganisms, is discussed as a model case.

Biodegradation, Environmental↗