Biomedical subjects

M Echeverría

Publications and source records attributed to M Echeverría.

8 recordsLinked to original sources

PubMed2004

Characterization of a crucifer plant pre-rRNA processing complex.

In cruciferous plants, the primary pre-rRNA cleavage site (P site) is immediately downstream of four similar, highly conserved sequences (A(1), A(2), A(3) and B) located within the 5'-ETS (5'-external transcribed spacer). In the present study, we describe the characterization of a plant NF D (nuclear factor D) that binds and interacts specifically with this A(123)BP cluster in the rDNA sequence. NF D is a high-molecular-mass complex containing nucleolin, fibrillarin and U3 and U14 snoRNAs. Furthermore, we show that NF D binds and cleaves pre-rRNA specifically at the P site. Thus we conclude that NF D is a pre-rRNA processing complex that may first assemble on rDNA and then bind nascent pre-rRNA.

Brassica↗

PubMed2001

Identification of 66 box C/D snoRNAs in Arabidopsis thaliana: extensive gene duplications generated multiple isoforms predicting new ribosomal RNA 2'-O-methylation sites.

Dozens of box C/D small nucleolar RNAs (snoRNAs) have recently been found in eukaryotes (vertebrates, yeast), ancient eukaryotes (trypanosomes) and archae, that specifically target ribosomal RNA sites for 2'-O-ribose methylation. Although early biochemical data revealed that plant rRNAs are among the most highly ribomethylated in eukaryotes, only a handful of methylation guide snoRNAs have been characterized in this kingdom. We report 66 novel box C/D snoRNAs identified by computational screening of Arabidopsis genomic sequences that are expressed in vivo from either single genes, 17 different clusters or three introns. At the structural level, many box C/D snoRNAs have dual antisense elements often matching rRNA regions close to each other on the rRNA secondary structure, which is reminiscent of their archaeal counterparts. Remarkable specimens are found that display two antisense elements having the potential to form an extended snoRNA-rRNA duplex of 23 to 30 nt, in line with the hypothetical function of box C/D snoRNAs in pre-rRNA folding or chaperoning. In contrast to other species, many Arabidopsis snoRNAs are found in multiple isoforms mainly resulting from two different mechanisms: large chromosomal duplications and small tandem duplications producing polycistronic genes. The discovery of numerous different snoRNAs, some of them arising from common ancestors, provide new insights to understand snoRNAs evolution and the birth of new rRNA methylation sites in plants and other organisms.

Arabidopsis↗

PubMed2000

Fibrillarin genes encode both a conserved nucleolar protein and a novel small nucleolar RNA involved in ribosomal RNA methylation in Arabidopsis thaliana.

Fibrillarin is a key nucleolar protein in eukaryotes which associates with box C/D small nucleolar RNAs (snoRNAs) directing 2'-O-ribose methylation of the rRNA. In this study we describe two genes in Arabidopsis thaliana, AtFib1 and AtFib2, encoding nearly identical proteins conserved with eukaryotic fibrillarins. We demonstrate that AtFib1 and AtFib2 proteins are functional homologs of the yeast Nop1p (fibrillarin) and can rescue a yeast NOP1-null mutant strain. Surprisingly, for the first time in plants, we identified two isoforms of a novel box C/D snoRNA, U60.1f and U60.2f, nested in the fifth intron of AtFib1 and AtFib2. Interestingly after gene duplication the host intronic sequences completely diverged, but the snoRNA was conserved, even in other crucifer fibrillarin genes. We show that the U60f snoRNAs accumulate in seedlings and that their targeted residue on the 25 S rRNA is methylated. Our data reveal that the three modes of expression of snoRNAs, single, polycistronic, and intronic, exist in plants and suggest that the mechanisms directing rRNA methylation, dependent on fibrillarin and box C/D snoRNAs, are evolutionarily conserved in plants.

Amino Acid Sequence↗

PubMed1997

Two ribosomal DNA-binding factors interact with a cluster of motifs on the 5' external transcribed spacer, upstream from the primary pre-rRNA processing site in a higher plant.

In radish the primary processing site in pre-rRNA has been mapped to a TTTTCGCGC sequence (motif P) in the 5' external transcribed spacer (5' ETS) of the ribosomal DNA (rDNA) [Delcasso-Tremousaygue, D., Grellet, F., Panabières, F., Ananiev, E. & Delseny, M. (1988) Eur. J. Biochem. 172, 767-776]. The processing site is just downstream of four similar motifs named A1, A2, A3 and B. The five motifs constitute cluster A123BP. We have described previously that in radish extracts a nuclear protein, nuclear factor B (NF B) specifically binds to motif B [Echeverría, M., Penon, P. & Delseny, M. (1994) Mol. Gen. Genet. 243, 442-452]. Here, by means of electrophoretic-mobility-shift assays, we describe an rDNA-binding activity, nuclear factor D (NF D), that interacts with the A123BP cluster. Using various rDNA probes and competitors we show that NF D binds specifically to the A123 clustered motifs but not to similar B or P motifs. We used sequence-specific DNA-affinity chromatography to separate NF D from NF B. DNase I footprinting was used to map the binding site of NF D on the A123BP cluster and we compared it with that of NF B on the same probe. The footprint of NF D extends from the A1 motif to the 5' end of the NF B-binding site and includes motifs A2 and A3 on each strand. The footprinting of NF B is restricted to motif B and adjacent nucleotides. Thus the NF D-binding and NF B-binding sites are distinct but overlap. These two factors bind with a high specificity to the A123BP cluster in the radish 5' ETS. The possibility that these factors regulate rDNA transcription elongation at the level of the primary pre-rRNA processing site in crucifers is discussed.

Base Sequence↗

PubMed1995

Multiresolution decomposition of non-stationary EEG signals: a preliminary study.

Wavelet representation is a recent development in the analysis of non-stationary signals. Its possibilities for use in the description of time-frequency characteristics of both transients in spontaneous EEG and time-varying rhythms in event related brain activity are explored here. By way of illustration, multiresolution decompositions of a wide variety of EEG transients are carried out in this work, including spike-and-waves, single spikes, sharp waves, blink artifacts, frontal intermittent rhythmic delta activity (FIRDA) and paroxysmal delta activity. Also, the application of the wavelet representation to study related spectra perturbations is illustrated with data from psychophysical experiments on the perception of image motion. The results demonstrate the capabilities of the wavelet transform, as an alternative to the Fourier transform, for the representation and analysis of non-stationary EEG signals.

Artifacts↗

PubMed1994

Plant ribosomal DNA external spacer binding factors: a novel protein binds specifically to a sequence close to the primary pre-rRNA processing site.

Sequence analyses of the ribosomal DNA (rDNA) external spacer region revealed a peculiar structure around the primary pre-rRNA processing site in radish. Using the electrophoretic mobility shift assay, DNAse I footprinting and methylation interference analysis, we have identified in radish extracts a novel nuclear factor, NF B, that recognises this region. NF B binds to a unique CGATTTTGCCCCTGA sequence located 164 bp downstream of the transcription initiation site and immediately upstream of the pre-rRNA processing site. Interestingly, this motif is flanked by four homologous sequences, including the primary pre-rRNA processing site, which are not recognised by NF B. Based on these data and the prediction that alternative hairpin loops can be formed in this region of the nascent pre-rRNA, a putative role for NF B as a factor coupling transcription and pre-rRNA processing is discussed. NF B is unique among plant and animal rDNA-binding proteins and it differs from a previously described radish factor and from other proteins that bind to plant rDNA promoters.

Base Sequence↗

PubMedDate not supplied

[Adolescent mothers].

Pregnancy during adolescence can be considered a health problem because it involves a greater risk, according to the WHO, for the health of mother and child. In this retrospective study an analysis was made of the socio-economic profile and the evolution of gestation and delivery of adolescent mothers attended by the Virgen del Camino hospital. A differentiation was made between two groups, with ethnic origin (Caucasian/Gypsy) taken as a variable, since it was considered that this determines the outcome of pregnancy. It was concluded that a high percentage had a partner and were under obstetric supervision and, probably for this reason, had had spontaneous deliveries, with a low index of prematurity. An association was also drawn between precocious maternity and urban environment or academic-occupational inactivity.

English Abstract↗

PubMedDate not supplied

[Current surgical indications for tonsillar pathology].

Tonsillectomy is one of the most controversial topics in otolaryngology. Today the immunologic role of the lymphoid tissue allows to clarify the surgical indications. Chronic bacterial tonsillitis, obstructive hypertrophic tonsils, peritonsillar abscess, suspicious of malignancy and fever convulsions produced by tonsillitis are the absolute indications for tonsillectomy. We review the literature on this topic.

Airway Obstruction↗