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Biomedical subjects

M S Valenzuela

Publications and source records attributed to M S Valenzuela.

At least 19 recordsLinked to original sources
PubMed1992

Adhesion to and invasion of cultured human cells by Bartonella bacilliformis.

Bartonella bacilliformis was tested for its ability to adhere to and invade tissue culture cell monolayers. The parasite was able to efficiently bind and penetrate human dermal fibroblasts, human laryngeal epithelium, and human umbilical vein endothelial cells. Exposure of the organism to immune serum prepared against a crude Bartonella extract containing cell wall and membranous material resulted in decreased ability of the parasite to invade host cells. There was also an overall reduction in the invasiveness of bartonellae and total host cell association when human laryngeal epithelial cells and human umbilical vein endothelial cells were preexposed to cytochalasin D, indicating an active involvement of host cells in the uptake of bartonellae. Transmission electron microscopy revealed the presence of bartonellae inside and outside intracellular vacuoles. These data suggest that a surface-associated factor is involved in the invasion process and that internalization of the parasite by host cells involves a microfilament-dependent process similar to phagocytosis.

Adhesins, Bacterial↗
PubMed1992

[Reproductive health survey of young adults in greater Santiago].

In 1988 a survey was carried out in order to obtain information on knowledge about reproduction, sexual activity, attitudes, and use of contraceptive methods among residents between 15 and 24 years of age in Greater Santiago. For this purpose, a multistage, self-weighted, non-replacement probability sample was chosen from the entire Santiago urban area. After 2,898 households were visited, 865 women and 800 men were selected and interviewed. For the interview, a questionnaire with 156 questions was developed; many questions were similar to those included in similar surveys in Brazil and Guatemala. The interviewers were professionals who had received prior training. Although 75% of the interviewees had attended sex education classes, they had erroneous ideas on various basic subjects. Sixty-nine percent of the women interviewed had undergone menarche before attending these classes. In addition, 35.4% of the women and 65.0% of the men had had sexual relations prior to marriage, and less than 20% had used any contraceptive method. More than 60% of the interviewees who had children had conceived them before marrying. These findings point up the necessity of offering sex education classes for children and young people, as well as facilitating their access to family planning services, in order to decrease the number of illegitimate and unwanted children that are born in Chile.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Catenated dimers and knotted DNA structures: putative intermediates in the replication of T. cruzi kinetoplast minicircle DNA.

Upon centrifugation of gently lysed T. cruzi cells through a sucrose gradient, a free DNA fraction was shown to contain catenated dimers and knotted DNA structures. Southern hybridization and electron microscopic studies indicated that both of these structures derived from minicircle DNA, the major component of T. cruzi kinetoplast DNA. Partial denaturation analysis of a random population of catenated dimers suggests that these structures may have arisen from a late stage in the replication of minicircle DNA. On the other hand, the T. cruzi knotted minicircles we have isolated appear to be very similar to trefoil structures recently reported and implicated as replicative intermediates in two other trypanosoma species.

Animals↗
PubMed1991

Survey of reproductive health in young adults, greater Santiago, 1988.

This article reports the results of an interview survey with 1,665 residents of Metropolitan Santiago 15-24 years old. The survey, which dealt with various aspects of reproductive health, indicated that the sex education received by 75% of the subjects generally failed to convey an accurate knowledge of the basic concepts of sexuality; that use of contraceptive methods was very limited; that approximately 25% of the 865 women interviewed had been pregnant at some time; and that 40% of all the pregnancies were unplanned. These findings demonstrate a need to begin effective sex education programs and to provide adolescent services commensurate with the circumstances of modern life.

Acquired Immunodeficiency Syndrome↗
PubMed1990

An autonomously replicating sequence from HeLa DNA shows a similar organization to the yeast ARS1 element.

A HeLa DNA fragment, which may function as an anchorage point to the nuclear matrix for human chromosomes 1 and 2, also functions as an autonomously replicating sequence (ARS) in the yeast Saccharomyces cerevisiae. In the present report we show that this DNA fragment contains both bent DNA and an A-T rich region which appear to be associated with the ARS function. More interestingly, DNA sequence analysis shows that the spatial distribution of these features is strikingly similar to that found in the yeast ARS1 element.

Base Sequence↗
PubMed1990

[Reproductive health survey in young adults: sexual experience and use of contraceptives in Santiago, Chile].

A self weighted, 2 stage probability sample of households in greater Santiago was obtained to select women and men between 15 and 24 years of age in order to obtain information about knowledge of sexual aspects, sexual activity and use of contraception. 35% of females and 65% of males declared to have had premarital sexual intercourse. Mean age at first premarital coitus was 18 and 16 years for women and men, respectively. Partners were 3.5 years older for females and 2.5 years older for males. A steady boy friend was the most common first sexual partner for females. Only 20% of women and 19% of males used contraception at first coitus. Rhythm, pills and withdrawal were the most commonly used methods. Less than 4 coituses in the 2 months preceding the survey were declared by 75% of subjects. All women declared themselves monogamous; 8% of males acknowledged more than one sexual partner in the last month.

Adolescent↗
PubMed1989

Bidirectional sequencing of supercoiled plasmid DNA.

In this paper we show that restriction DNA fragments can prime DNA synthesis of a homologous supercoiled plasmid DNA. Using the dideoxyribonucleotide chain terminator method, newly synthesized truncated chains can be detached from the primers by restriction enzyme digestion. Therefore, by choosing DNA fragments flanked by two different restriction enzymes sites, nucleotide sequence information can be simultaneously obtained on both regions of the DNA surrounding the restriction fragment. The advantage of this sequencing approach over current methods is that no prior knowledge of the primary sequence is needed to find the nucleotide sequence of a given DNA fragment. Thus, synthetic primers are not required and internal sequences of a given clone can be easily accessed without the need of fragmenting the original construct. The method has been used with rapid plasmid preparations, thus considerable time and effort can be saved in the gathering of nucleotide sequence information.

Base Sequence↗
PubMed1989

A unique deletion in pBR322 DNA caused by insertion of poly(dA).poly(dT).

A unique deletion covering around 43% of the pBR322 genome was found after attempting to insert 100 or 200 bp poly(dA).poly(dT) into the EcoRV site of pBR322 DNA. This result was not observed if an equivalent size heterologous DNA or a larger poly(dA).poly(dT) fragment of 10-20,000 bp was introduced at the same site. DNA sequencing analysis at the junctions suggests that a specific intramolecular pairing may be involved in the formation of this deletion mutant.

Base Sequence↗
PubMed1989

Chromosomal mapping and nucleotide sequence of a human DNA autonomously replicating sequence.

A 1.1-kb human DNA fragment (ARSH1) capable of functioning as a putative origin of replication in yeast cells has been characterized both by in situ hybridization to human metaphase chromosomes and by DNA sequencing. Our hybridization studies show a preferential localization of ARSH1 in chromosome regions 1p34-36 and 2q34-37. DNA sequence analysis indicates that in addition to the consensus sequence required for ARS function in yeast cells, nuclear matrix-associated DNA motifs are also present in the 1.1-kb fragment. These results suggest that ARSH1 sequences may serve as points of anchorage to the nuclear matrix for chromosomes 1 and 2.

Amino Acid Sequence↗
PubMed1987

Enriched autonomously replicating sequences in a nuclear matrix-DNA complex isolated from synchronized HeLa cells.

Nucleoids isolated from either synchronized or exponentially growing HeLa cells were digested with restriction enzymes to separate a nuclear matrix-bound DNA component from the rest. Partial libraries were constructed by inserting DNA fragments from both components into a yeast-bacteria plasmid vector. A random sample from these libraries was tested for ARS activity by a standard yeast transformation assay. We found that synchronization for DNA replication results in an enrichment for autonomously replicating sequences in the library constructed with the DNA component bound to the nuclear matrix.

Base Sequence↗
PubMed1986

Multiply branched DNA molecules from bacteriophage lambda: putative post-replicational repair DNA intermediates.

Previous studies have shown that thymidine deprivation causes the formation of multiply branched molecules among bacteriophage lambda DNA replicative intermediates. In the present report, we present supporting evidence indicating that the induction of the SOS response is involved in this process. Moreover, close inspection of the DNA replicatives intermediates present in a recA deficient strain, shows an accumulation of gapped replicative intermediates. From these observations we postulate a model by which multiply branched DNA molecules may be intermediates or derived intermediates of a post-replicational repair pathway.

Bacteriophage lambda↗
PubMed1981

Direction of bacteriophage lambda DNA replication in a thymine requiring Escherichia coli K-12 strain. Effect of thymidine concentration.

The direction of replication was established for the first round of bacteriophage lambda DNA replication in thymine requiring E. coli K-12 cells exposed to different concentrations of thymidine. It was found that a dramatic decrease in the proportion of bidirectionally replicating molecules followed a decrease in the concentration of thymidine. Moreover, the rightward mode of replication appears to be exclusively favored in unidirectionally replicating molecules found at low concentrations of thymidine.

Bacteriophage lambda↗
PubMed1981

Isolation of DNA fragments containing replicating growing forks from both E. coli and B. subtilis.

By the use of a restriction enzyme digestion of gently lysed E. coli or B. subtilis cells, it is possible to isolate a minute fraction of the total DNA that has an unusually high sedimentation coefficient. Upon inspection of this DNA in the electron microscope, branched DNA fragments are observed. Single branched DNA fragments were analyzed by restriction enzyme and partial denaturation mapping techniques. The fragments appear to have the properties of growing forks excised from in vivo replicating intermediates. In B. subtilis, the minute fraction of DNA was also investigated by transformation assays and found to be greatly enriched for a marker near the origin and slightly enriched for a terminus marker.

Bacillus subtilis↗
PubMed1981

Multiply branched replicative intermediates in E. coli and bacteriophage lambda.

Multiple branched DNA fragments present in a fast sedimenting complex comprising a minute fraction of the E. coli genome have been isolated. Similar structures were also observed among bacteriophage lambda DNA replicative intermediates after infection of synchronized E. coli cells. These structures were found to be associated with the amino acid and thymidine starvation steps required for synchronization and originate either by initiation from secondary sites or by snap-back of daughter strands containing substantial single stranded regions in the vicinity of the growing point.

Bacteriophage lambda↗
PubMed1978

Restriction enzyme cleavage of DNA resulting from gently lysed Escherichia coli.

When E. coli or lambda infected E. coli are gently lysed the DNA is released as a very fast sedimenting species that is presumably bound to membrane material. If this complex is now subjected to restriction enzyme cleavage, only a minor fraction of the fast sedimenting DNA remains and this is found, after purification, to be enriched for branched molecules.

Cell Membrane↗