Biomedical subjects

S Ballester

Publications and source records attributed to S Ballester.

8 recordsLinked to original sources

PubMed1992

Genetic alterations by human papillomaviruses in oncogenesis.

The integration sites in the cellular genome of human papillomavirus are located in chromosomal regions always associated with oncogenes or other known tumor phenotypes. Two regions, 8q24 and 12q13, are common to several cases of cervical carcinoma and can have integrated more than one type of papillomavirus DNA. These two chromosomal regions contain several genes implicated in oncogenesis. These observations strongly imply that viral integration sites of DNA tumor viruses can be used as the access point to chromosomal regions where genes implicated in the tumor phenotype are located, a situation similar to that of non-transforming retroviruses.

Chromosomes, Human, Pair 12↗

PubMed1991

Influence of PCR parameters on amplifications of HIV-1 DNA: establishment of limiting sensitivity.

We have investigated the optimal reaction conditions and the limiting sensitivity for detection of HIV-1 DNA by PCR. The amplification systems studied were gag (SK38/SK39); pol (P3/P4); and two other systems described here for the first time, LTR (LTR1/LTR2) and nef (Nef1/Nef2), which amplify fragments of 115 bp, 308 bp, 632 bp and 643 bp, respectively. Two PCR profiles were assayed, and the requirements for deoxynucleoside triphosphate and MgCl2 concentrations for each amplification reaction were determined. Optimal reaction conditions were oriented toward selecting maximal amplification of the expected size fragment. Limiting sensitivity was estimated by testing the decreasing copy number of a plasmid containing HIV-1 genome and obtaining a positive amplification signal with at least 5, 5, 10 and 5 copies for LTR, gag, pol and nef, respectively. We conclude that the establishment of the detection sensitivity on a PCR is an important parameter to be considered for the interpretation of results on HIV-1 infection.

Base Sequence↗

PubMed1990

Comparative expression of the pC194 cat gene in Streptococcus pneumoniae, Bacillus subtilis and Escherichia coli.

The expression of the cat gene of the staphylococcal plasmid pC194 present in the pLS1-pC194 composite plasmid pJS37 was lower in Streptococcus pneumoniae and Escherichia coli than in Bacillus subtilis. Different transcription start points (and, by inference, different promoter utilization) of the cat mRNA synthesized in S. pneumoniae or B. subtilis were detected. Plasmid pJS37 is prone to deletion formation when host cells are grown in the presence of chloramphenicol (Cm). The analysis of the expression of the cat gene carried by the deleted derivatives of pJS37 has shown that a new promoter for the synthesis of cat mRNA is involved in the selective advantage conferred to the host by those deleted plasmids. Characterization of either in vivo or in vitro deleted plasmids has shown that the nucleotide sequence that could encode for a putative leader peptide is required for the Cm-induced pC194 cat gene expression.

Amino Acid Sequence↗

PubMed1989

Plasmid structural instability associated with pC194 replication functions.

The hybrid plasmid pJS37 is composed of the streptococcal plasmid pLS1, which confers tetracycline resistance, and the staphylococcal plasmid pC194, which confers chloramphenicol resistance. When gram-positive bacteria containing pJS37 were grown in the presence of chloramphenicol, four different deleted derivatives accumulated. The deletions in the plasmid enhanced resistance to chloramphenicol by placing the cat gene of pC194 near promoters of pLS1. All four deletions shared a common endpoint that corresponded to the putative target site for DNA strand nicking by the pC194 replication protein, RepH. At the other, variable endpoint, the DNA sequence was similar to the putative RepH target sequence. Alteration of the RepH protein, by in vitro modification of the gene encoding it, eliminated this class of deletions. By extending a previously proposed model for the generation of a different but related class of deletions (B. Michel and S.D. Ehrlich, EMBO J. 5:3691-3696, 1986), a comprehensive model that could generate both classes of deletions is suggested. It proposes that a nicking-closing activity of the plasmid replication protein at its normal target site and, aberrantly, at sites with similar sequence can generate deletions either proximal or distal to the aberrant site during rolling-circle replication of the plasmid.

Bacterial Proteins↗

PubMed1986

Selective advantage of deletions enhancing chloramphenicol acetyltransferase gene expression in Streptococcus pneumoniae plasmids.

A hybrid plasmid, pJS37, was made by combining pLS1, which confers tetracycline (Tc) resistance, and pC194, which confers chloramphenicol (Cm) resistance. Both pJS37 (7.3 kb) and its derivative pJS140 (6.0 kb), from which pC194 replication genes were removed, were structurally and segregationally stable when introduced into Streptococcus pneumoniae and grown either in the presence of Tc or in the absence of drug. However, both hybrid plasmids underwent systematic deletion when grown in the presence of Cm. One of the deleted forms, pJS4 (3.4 kb), could not be maintained in the absence of a helper plasmid; two others, pJS3 (4.1 kb) and pJS5 (3.8 kb), lost the tet gene but retained the replication functions of pLS1. They both expressed very high levels of Cm acetyltransferase (CAT), which, in the case of pJS5, were constitutive. Nucleotide sequence determination of the deletion junctions in pJS3 and pJS5 indicated that the deletions occurred, presumably by recombination, between short direct repeats of 6 and 9 bp, respectively. In both cases the tet promoter was juxtaposed to the cat gene. In the case of pJS5, the deletion removed a sequence that sequestered the ribosome-binding site (RBS) for cat, thereby rendering constitutive the production of CAT. The increased resistance to Cm afforded by the hyperexpression of the cat gene apparently provided a positive selective advantage for the accumulation of the deleted forms in the plasmid pool.

Acetyltransferases↗

PubMed1986

Inhibition of transformation of Bacillus subtilis by ethidium bromide.

Incubation of donor DNA with ethidium bromide before addition to competent cells, strongly inhibited chromosomal transformation, plasmid transfer and phage-SPP1 DNA mediated transfection. There was no effect of the dye on the binding and entry of DNA into the cells. Analysis of the fate of transforming DNA treated with ethidium bromide showed a reduction in the amount of donor DNA associated with the recipient chromosome. The formation of this donor-recipient complex seems to be slowed down by the dye.

Bacillus subtilis↗

PubMed1985

Binding of transforming DNA to protoplasts isolated from competent Bacillus subtilis.

Transforming 3H-labelled DNA binds specifically to protoplasts isolated from competent cultures of Bacillus subtilis. The bound DNA is fully accessible to added DNase I, indicating that protoplasts bind, but do not process donor DNA. A bi-phasic pattern of competition for binding with increasing amounts of unlabelled and labelled DNA was found. In these conditions, two levels of saturation appeared which correspond to two kinds of DNA receptor sites. Homologous DNA binds preferentially to the first kind of receptor (specific) and only at higher concentrations would bind to the second (unspecific) binding sites. Bound DNA forms a rather stable complex with some constituent(s) of the protoplasts.

Bacillus subtilis↗

PubMed1983

Transformation in Bacillus subtilis: different affinities for DNA-binding to competent cells and to membrane vesicles.

Comparison between dose-response curves to homologous and to T*4 (non-glucosylated) DNA in cells and in membrane vesicles, isolated from competent Bacillus subtilis, indicated the presence of two kinds of DNA receptors in the membrane vesicles system. This was confirmed by competition experiments. In addition, concentration dependence for binding of low-molecular weight homologous DNA also revealed the existence of more than one DNA receptor site in competent cells of B. subtilis. However, no differences in the uptake of sheared or intact DNA was observed, which indicates that only one kind of receptors is involved in the entry of donor DNA. Competition experiments in binding, uptake, and transformation, with the possible combinations of sheared or intact DNAs, suggested that the former has more affinity for the binding sites than the latter. This finding is also supported by the results obtained in membrane vesicles, either in competition or in chasing experiments.

Bacillus subtilis↗