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Biomedical subjects

L Caro

Publications and source records attributed to L Caro.

At least 55 records · Page 3Linked to original sources
PubMed1981

[Trophic and functional changes of the pancreas induced by chronic truncal vagotomy].

The effects of chronic truncal vagotomy on the pancreatic gland was studied in male adult Wistar rats. Two to three months after parasympathetic decentralization, the gland weight was found to be significantly increased by nearly 100%. This trophic effect is mainly due to the proliferation of young acinar cells. Concomitantly, there is a decrease of the ductular mass and of the Langerhans islets. Choline acetylase activity was decreased by about 35% to 40% in the vagotomized pancreas. Further, enzyme concentration was found to be greater in the head than in the body and tail of the gland, thus suggesting a higher nerve density of vagal cholinergic fibers in the former than in the latter. Basal pancreatic secretion of the decentralized gland showed a significant increase in the flow rate with no significant changes in both bicarbonate concentration and output. Protein concentration was significantly reduced at 60 minutes; protein output remained unchanged. The most remarkable finding was the fall in both lipase concentration and output (60-70%) when compared with control values. These findings may be related to clinical manifestations after long-term vagotomy.

Animals↗
PubMed1980

Isolation of an IS1 flanked kanamycin resistance transposon from R1drd19.

We have isolated and identified an IS1-flanked transposon from the plasmid R1drd19. This transposon specifies resistance to kanamycin and is 10.4 kg long. It exhibits a frequency of transposition two orders of magnitude lower than that of the smaller, IS1-flanked transposon Tn9. We have named it Tn2350.

DNA Transposable Elements↗
PubMed1980

Production of extrachromosomal r-determinant circles from integrated R100.1: involvement of the E. coli recombination system.

The drug resistance plasmid R100.1 can integrate into the E. coli chromosome at several sites on the plasmid. Many of the resulting Hfr strains continuously produce extrachromosomal circular forms of the r-determinant. These r-det 'plasmids' seem incapable of stable autonomous replication. We show that their presence in the cell requires the continuous activity of functional recA and recC genes but does not require the lexA function. The production of r-det circular forms is correlated with an increased copy number of r-det sequences, relative to RTF sequences, This copy number increase is, however, also found in a recA- background where no circular forms of r-det are found. These results show that a specific replication of r-det sequences, not present in the wild-type R100.1 plasmid, occurs in these R-Hfr strains. They suggest that a rec promoted recombination, posterior to the specific replication event, is needed for the production of circular r-det forms.

DNA Replication↗
PubMed1979

Some properties of the chloramphenicol resistance transposon Tn9.

We have isolated variants of the plasmid RTF which have received the transposon Tn9 from bacteriophage P1Cm. We have shown by the formation of heteroduplex molecules between one RTF:Tn9 derivative and R100.1 that Tn9 is homologous to the r-determinant region of R100.1 which carries the determinants for chloramphenicol resistance. This suggests that Tn9 was derived from an r-det like structure by deletion, possibly mediated by one of the flanking IS1 elements. In spite of the similarity in structure between Tn9 and r-det however, we have demonstrated two distinct differences in the behavior of these two elements: 1) Tn9 but not r-det, is able to amplify, by a recA dependent mechanism, when cells harboring RTF::Tn9 are grown in the presence of chloramphenicol, and 2) Tn9, unlike r-det, does not form extrachromosomal circular molecules when RTF::Tn9 is tegrated into the bacterial chromosome.

Chloramphenicol↗
PubMed1979

The effects of an Escherichia coli dnaAts mutation on the replication of the plasmids colE1 pSC101, R100.1 and RTF-TC.

The rate of replication of the plasmids colE1, pSC101, R100.1 and pAR132 (an RTF-TC derivative of the drug resistance factor R100.1) has been investigated directly by DNA:DNA hybridization. These rates have been compared, in a dnaAts strain, to that of various markers of the host chromosome at permissive and non-permissive temperatures. Chromosome initiation in the dnaAts strain stops rapidly after a shift to the non-permissive temperature, but plasmids R100.1 and pAR132 do not seem to be affected directly and continue replication for some time. The colE1 replication rate undergoes a large increase after the temperature shift, followed by a rapid decrease to a very low level 25 min after the shift. In contrast pSC101 replication stops immediately after the shift. ColE1 is able to replicate in an integratively suppressed dnaAts strain at 42 degrees C whereas pSC101 stops replication immediately under these conditions. We conclude that R100.1 and its derivative RTF-TC can replicate without a functional dnaA product; that colE1, while affected by a shift in temperature in a dnaAts strain, does not directly require dnaA; and that the plasmid pSC101 has an absolute requirement for dnaA. The absolute requirement of pSC101 for dnaA in the integratively suppressed Hfr strain provides a useful system for further investigation of the dnaA function.

DNA Replication↗
PubMed1979

Tn10 mediated integration of the plasmid R100.1 into the bacterial chromosome: inverse transposition.

Upon integration into the bacterial chromosome the drug resistance plasmid R100.1 often loses its tetracycline resistance character. We have analyzed an Hfr strain formed by such an integration and an R-prime plasmid derived from it. We find that integration took place within the Tn10 transposon, that the two IS10 sequences were retained, but that at least 80% of the transposon segment located between them, and carrying the tetracycline resistance genes, had been lost. We suggest that integration of R100.1 was mediated by an inverse transposition using the IS10 sequences.

Chromosomes, Bacterial↗
PubMed1978

A cold sensitive dnaA mutant of E. coli which overinitiates chromosome replication at low temperature.

A heat resistant mutant of E. coli dnaAts46 was isolated, which grows normally only at temperatures above 39 degrees. After a temperature shift from 42 degrees to 32 degrees the mutant overproduces DNA relative to protein. This is due to overinitiation of rounds of chromosome replication at low temperature, as indicated by hybridization and other experiments. The mutation is cotransduced by PI with ilv and could not be separated from dnaAts46 by transduction.

Chromosome Mapping↗
PubMed1977

Involvement of IS1 in the dissociation of the r-determinant and RTF components of the plasmid R100.1.

The formation of the r-determinant pLC1 and of the RTF pAR132 from the composite plasmid R100.1 was investigated. The general location of IS1 sequences on the three plasmids was established by hybridization of lambdar14 CII::IS1 DNA to EcoRI generated fragments of the various plasmids separated by agarose gel electrophoresis and transferred directly to nitrocellulose filters. The position of IS1 sequences on these fragments and the homologies between fragments were analyzed by electron microscopy of heteroduplex molecules. The results show that the excision of both pLC1 and pAR132 occurred by an exchange between the two IS1 sequences present on R100.1.

Base Sequence↗
PubMed1977

Replication of prophage P1 during the cell cycle of Escherichia coli.

We have followed, by DNA-DNA hybridization, the variation in the number of copies of prophage P1 relative to two chromosomal markers when the doubling time of the host cells is modified by a change in carbon source. The ratio of P1/chromosome terminus undergoes a twofold decrease when the cell doubling time increases from 24 to 215 min, whereas the ratio of P1/chromosome origin increases 1.4 fold; both ratios tend towards unity at slow growth rates. This suggests that the replication of prophage P1 is not simultaneous with chromosome initiation or chromosome termination. The chromosome replication time is unaffected by the presence of P1, and remains constant over the range of doubling times studied, with a value of about 4o min. Following amino acid starvation, the P1/chromosome origin ratio increases from 0.7 to 0.9, suggesting that P1 retains the ability to replicate after chromosome initiation has stopped and in the absence of essential amino acids. The results are discussed with reference to similar studies done on F and R1.

Cell Division↗
PubMed1977

Suppression of an Escherichia coli dnaA mutation by the integrated R factor R100.1: generation of small plasmids after integration.

We have observed that integration of the R plasmid R100.1 into the chromosome of Escherichia coli is associated with the formation of small, covalently closed circular elements. Contour length measurements, partial denaturation mapping, and analysis of the deoxyribonucleic acid fragments produced by digestion of one of these, pLC1, with the restriction endonuclease EcoRI indicate that it is the r-determinant element of R100.1.

Chromosomes, Bacterial↗
PubMed1977

Suppression of an Escherichia coli dnaA mutation by the integrated R factor R100.1: origin of chromosome replication during exponential growth.

We have investigated the behavior, during exponential growth, of strains of Escherichia coli carrying a dnaA(Ts) mutation that has been suppressed by the integration of the F-like R plasmid R100.1. We present evidence showing that replication in these strains proceeds largely from the normal chromosome origin at 30 degrees C, a permissive temperature for the dnaA(Ts) gene product, whereas, at 42 degrees C, replication proceeds largely from the integrated plasmid. These conclusions are based on measurements made by deoxyribonucleic acid:deoxyribonucleic acid hybridization of the relative frequencies of the prophages Mu-1 and lambdaind- and R100.1 integrated at known locations on the E. coli chromosome in these Hfr strains.

Chromosome Mapping↗
PubMed1977

Origin and direction of replication of the drug resistance plasmid R100.1 and of a resistance transfer factor derivative in synchronized cultures.

The origin and direction of replication of the resistance plasmid R100.1 and its resistance transfer factor derivative, pAR132, were studied by electron microscopy autoradiography of partially denatured molecules and partial denaturation mapping of replicative intermediates. Results of these studies indicate the existence of an origin of replication at 8.8 kilobases on the R100 map. Replication from this origin in cultures synchronized for initiation of replication is predominantly unidirectional in a single direction.

Amino Acids↗
PubMed1976

Suppression of an Escherichia coli dnaA mutation by the integrated R factor R.100.1: Change of chromosome replication origin in synchronized cultures.

We have followed, by deoxyribonucleic acid-deoxyribonucleic acid hybridization, the order of replication of three chromosomal markers during a synchronous round of replication in three strains of Escherichia coli carrying a dnaAts mutation: one strain in which the F-like R factor R.100.1 was established as a plasmid and two strains in which the dnaA mutation was suppressed by the integration of R.100.1 into the chromosome. In the R+ strain at 30C, replication of the plasmid took place simultaneously with the initiation of chromosome replication at the normal origin. In the integratively suppressed Hfr strains, at 42.5 C, chromosome replication was initiated preferentially from the integrated plasmid; little or no initiation occurred at the normal origin. Similar results were obtained for the one strain tested at 30 C. For both Hfr strains at 42.5 C, the data suggest that at least part of the population replicated bidirectionally. This conclusion had been confirmed using an autoradiographic procedure. Both types of experiment indicate a wide variation in the rate of travel of individual replication forks within the population.

Cell Division↗