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Biomedical subjects

A Favre

Publications and source records attributed to A Favre.

155 records · Page 9Linked to original sources
PubMedDate not supplied

Localization of the large subunit of replication factor C near the 5' end of DNA primers.

Replication factor C (RFC) is a heteropentameric sliding clamp loader protein essential for processive synthesis of DNA by eukaryotic DNA polymerases delta and epsilon. To study the interaction of RFC with 3' and 5' ends of the DNA primer, we have developed chemical photocrosslinking assay using a synthetic DNA gap and DNA primer-template structures. We have found that the radioactively labeled primers containing a photoreactive group at their 5' end could crosslink with the largest RFC subunit (RFC140) on primer-templates and DNA gap structures, but that 3' end photoreactive primers could only crosslink with RFC140 within the DNA gap structure. Addition of replication protein A (RPA) to the reaction mixture resulted in the crosslinking of RPA subunits and inhibited crosslinking of RFC140 using 3' but not 5' photoreactive primers present at the gap. The results suggest specific contacts between RFC140 and the 5' end of the DNA primer. Together with previous data, these experiments allow us to propose a model for the DNA polymerase switch during eukaryotic DNA replication.

5' Flanking Region↗
PubMedDate not supplied

Partial deproteinization of ribosomal subunits by treatment with high concentrations of sodium chloride: physical and chemical characterization of protein depleted particles.

Sedimentation of E. coli ribosomal subunits through sucrose gradients containing high concentrations of NaCl (0.1 - 1.0 M) brings about removal of a specific fraction of their proteins. The alterations in the structural properties of the subunits caused by dissociation of these proteins are studied. They appear to be, at least partly the result of removal of constraints on RNA conformation imposed by the released proteins.

Centrifugation, Density Gradient↗
PubMedDate not supplied

Mutagenesis and growth delay induced in Escherichia coli by near-ultraviolet radiations.

The literature relating to genetic changes induced in Escherichia coli by near-ultraviolet radiations is reviewed and summarized: i) these radiations are much less mutagenic than would be expected from the known level of DNA damage, ii) pre-illumination with near-UV light antagonizes the mutagenic effect of UV (254 nm) light. In agreement with these findings, the SOS functions are not induced by near-UV radiations. Furthermore prior exposure of cells to near-UV light inhibits the subsequent 254 nm induction of the SOS response. Among the several hypothesis considered to explain these observations, one can be clearly favoured. Near-UV light triggers, at sublethal fluences, the growth delay effect. The target molecules, tRNAs, are photocrosslinked and some tRNA species become poor substrates in the acylation reaction. In vivo these tRNA molecules accumulate on the uncharged form, leading to a transient cessation of protein synthesis. The SOS response is inducible and as such requires protein synthesis. We therefore propose that near-ultraviolet radiations have a dual effect: i) they induce, mostly indirectly, DNA lesions which are potentially able to trigger the SOS response, ii) they prevent the expression of the SOS functions through the transient inhibition of protein synthesis (growth delay).

Bacterial Proteins↗
PubMedDate not supplied

Synthesis of base-substituted dUTP analogues carrying a photoreactive group and their application to study human replication protein A.

Analogues of dUTP bearing a photoreactive 2-nitro-5-azidobenzoyl (NAB) group linked via spacers of varying length (n = 2, 4, 7-13 atoms) to the 5-position of the uridine ring (NAB-n-dUTP) were synthesized and characterized. DNA polymerase beta efficiently incorporated these analogues into synthetic primer-template substrates in place of TTP, which allowed us to selectively introduce a photoreactive group at the 3' primer terminus. After completing photoreactive primer synthesis, the reaction mixtures were irradiated with monochromatic UV light (315 nm) in the presence of human replication protein A (RPA), a heterotrimer consisting of three subunits with molecular mass 70 kDa (p70), 32 kDa (p32), and 14 kDa (p14), and were separated by SDS-PAGE. The photoreactive primers cross-linked directly with p70 and p32, but cross-linking of p14 was not achieved even by varying the length of the spacer group. The data speak in favor of the protection of p14 by other RPA subunits from the interaction with 3'-end of the primer. Cross-linking of substrates to pol beta is inhibited when the analogue bears a short spacer (n = 2, 4, 7, and 8), but this is abrogated somewhat when longer spacers (n = 9-13) are examined. On the basis of these observations, we suggest that RPA and pol beta form a complex on primer-template substrates.

Base Sequence↗
PubMedDate not supplied

Diet, length of gestation, and fecal short chain fatty acids in healthy premature neonates.

BACKGROUND: Excretion of fecal short-chain fatty acids (SCFAs) may indicate changes in colonic or colonocyte metabolism. The aim of this study was to detect the influence of gestational age and feeding practices on SCFA concentrations and profiles in healthy preterm infants. METHODS: A total of 198 fecal samples (28 infants) were collected from 8 to 21 days of age from 3 groups of preterm infants born at 33 to 37 weeks of gestation and fed either breast milk (group I) or Nutramigen, a lactose-free formula (group II), and extremely preterm infants born before 33 weeks of gestation and fed breast milk (group III). Total SCFA concentrations and SCFA profiles were analyzed using a gas chromographic (GC) procedure. RESULTS: Total fecal SCFA excretion did not differ significantly between group I (mean, 24.0 micromol/g; range, 1.3 to 118.8 micromol/g) and group II (mean, 23.0 micromol/g; range, 3.0 to 73.3 micromol/g). Conversely, differences occurred between SCFA profiles and became significant after day 17. The main differences were a significant increase in the butyric acid concentration (12% versus 30%) with group II. Compared with group I, fecal SCFA concentrations were 3.2-fold lower (7.4 micromol/g; range, 0.3 to 37.4 micromol/g) in group III with no significant changes in the profiles. CONCLUSIONS: Fecal SCFA excretion may vary in absence of any digestive disease. During this study, in terms of gestational age, total SCFA concentrations were significantly lower in extremely premature infants compared with infants born less premature, despite their known higher deficiency in intestinal lactase activity. In terms of diet, the absence of lactose did not lead to a decrease in colonic fermentation and induced changes in SCFA patterns. These new baseline data may offer clues to further development of milk formulas.

Age Factors↗
PubMedDate not supplied

Fecal short-chain fatty acids predict digestive disorders in premature infants.

BACKGROUND: Excretion of fecal short-chain volatile fatty acids (SCFAs) may indicate changes in colonic or colonocyte metabolism. The aim of this study was to detect the existence of an average fecal SCFA profile and to define which changes were associated with clinical events that occurred during the survey period. METHODS: SCFA profiles of 185 stool samples collected from 46 fed preterm neonates (mean birth weight, 1920 g; mean gestational age, 32.8 weeks) were evaluated and their association with digestive disorders or therapy was explored. RESULTS: Total SCFA concentration increased from 0 to 80 micromol/g feces wet weight over the first 20 days of life. A basic SCFA profile revealed the existence of a highly sensitive period between the second and the third week of life. In the absence of any digestive problem (n = 15), the butyric acid (C4) ratio increased from 7% to 24%. Phototherapy (n = 13) enhanced the SCFA concentration but decreased the ratios of C4 and minor acids. Digestive disorders reported included abdominal distention (n = 6) or bleeding (n = 8). Only in the case of bleeding was the SCFA profile changed by an enhancement of C4 by >50%. Antibiotic therapy (n = 3) suppressed SCFA production. CONCLUSIONS: This study supports a hypothesis that changes in the SCFA profile could offer a noninvasive method to anticipate functional modifications of the gastrointestinal tract before the first clinical signs of pathologic events, including necrotizing enterocolitis.

Anti-Bacterial Agents↗
PubMedDate not supplied

Cytotoxicity in vitro and preliminary antitumor activity in vivo of a novel organotin compound.

The cytotoxic effect and antitumor activity induced by the novel organotin compound triethyltin(IV)lupinyisulfide hydrochloride, have been investigated. Different patterns of antiproliferative effects have been observed in a panel of human tumor cell lines in vitro. Toxicity studies in mice reported acute toxicity at the doses of 21 and 17.5 mg/kg which progressively disappeared at lower concentrations. On this basis, the doses of 3.5, 7 and 14 mg/kg were selected to assess the antitumor activity in vivo against the P388 leukemic cells xenografted in mice. This compound was able to induce a dose-dependent significant reduction of tumor volume, up to 46%, at the highest concentration (p = 0.0062) without important toxicity, as also confirmed by histological analysis of the main organ tissues. This preliminary study seems to hold interest for further investigations in different tumor models as well as for the evaluation of optimal drug route and schedule.

Animals↗