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Biomedical subjects

L Cervantes

Publications and source records attributed to L Cervantes.

8 recordsLinked to original sources
PubMed1990

Characterization of two DNA populations of Giardia lamblia.

Total DNA was isolated from the parasitic protozoan Giardia lamblia and separated into two distinct populations of different densities by centrifugation through CsCl gradients containing Hoechst dye 33258. The two populations obtained were characterized by restriction enzyme analysis and nucleic acid hybridization. The less-dense population contains non-repetitive DNA and may encode mainly structural genes, such as those for alpha- and beta-tubulin. Digestion of the DNA with several restriction endonucleases showed that the denser band was composed of a 5.5 kb unit which contains the G. lamblia ribosomal RNA cistron in tandem repeated organization.

Animals↗
PubMed1988

Cloning, sequencing, and expression in Ficoll-generated minicells of an Escherichia coli heat-stable enterotoxin gene.

The gene encoding a heat-stable enterotoxin of Escherichia coli was cloned as a 960-bp fragment from a plasmid isolated from a Mexican strain of human origin. Deoxyribonucleotide sequencing unveiled a 216-bp open reading frame similar to that of a previously sequenced ST-toxin gene. The gene is preceded by a proposed binding site for the cAMP-mediated positive regulator (CAP) that is part of a 23-bp inverted repeat. The proposed CAP site is followed by a 6A, 1T, and 6A deoxyribonucleotides. Minicells containing the toxin gene, which were isolated from Ficoll gradients, shown to preserve the localization of intracellular and periplasmic enzymes, allowed the detection of a biosynthetically radiolabeled polypeptide with an apparent Mr 8400. The data suggest that the enterotoxin genes estA2, estA3, and estA4 are very similar, even in clinical strains isolated from distinct geographical locations; that the transcription of heat-stable enterotoxin genes is controlled by the cAMP-mediated positive regulatory system, and that the heat-stable enterotoxins are initially synthesized as 72 amino acid precursors to yield the extracellular active 18-19 amino acid polypeptides.

Amino Acid Sequence↗
PubMed1987

Electron microscopy and biochemical properties of polyamine-compacted DNA.

We have obtained polyamine-compacted DNA and analyzed it by electron microscopy employing the method described by Dubochet, suitable for the study of complexes in which the main interactions are of ionic character. In addition, we have developed a simple biochemical method, based on the action of pancreatic DNase I, to demonstrate the condensation of DNA with spermidine. DNA-spermidine complexes are resistant to the action of DNase I, and there is a strong correlation between the presence of condensed DNA forms, both as toroids and as cylinders, and the insensitivity to DNase I activity. We have also shown that pBR322 DNA-spermidine complexes are transcriptionally active in the presence of Escherichia coli RNA polymerase. This supports the data concerning the biological activity of spermidine-condensed DNA.

DNA↗
PubMedDate not supplied

Construction and characterization of new cloning vehicles. V. Mobilization and coding properties of pBR322 and several deletion derivatives including pBR327 and pBR328.

A DNA sequence essential for the R64drd11 + ColK-mediated conjugal transfer of pBR322 has been located in a 540 bp HaeIII fragment (HaeIII-2) between the vegetative origin of replication and the tetracycline resistance (Tcr) gene of this vector. The pBR322 derivatives pBR327 and pBR328 lack this DNA sequence and are not mobilized by conjugation. Two derivatives of pBR328 were constructed by re-inserting the HaeIII-2 fragment in both orientations into the chloramphenicol-resistance gene of the same vector. One orientation of the HaeIII-2 fragment permitted mobilization by conjugation while the opposite orientation prevented mobilization. Further examination of pBR322 and derivatives revealed that the region between the origin of replication and Tcr gene also plays a role in regulating plasmid copy number.

Bacterial Proteins↗