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At least 163 records · Page 9Linked to original sources
PubMed1986

Zinc oxide to induce molt in layers.

The effects of the addition of Zn as ZnO to diets to induce molt were evaluated against a fasted control. Experiment 1 involved 315 Leghorn hens, 15 months old, randomly distributed among five treatments, each replicated seven times with 9 hens per replicate. Hens fasted for 10 days were compared with hens fed diets to which ZnO was added at 10,000, 5,000, or 2,500 ppm for 7, 14, or 21 days. No significant differences were observed among treatments for days to return to 50% production, hen-day and hen-housed production, egg weight, grams egg per hen-day, grams of feed per gram egg, mortality, or Haugh units during the 22-week experimental period. Experiment 2 involved 420 Leghorn hens, 18 months old, randomly distributed among five treatments, each replicated seven times with 12 hens per replicate. Treatments involved fasting for 10 days or feeding diets with 10,000, 5,000, or 2,500 ppm ZnO fed for 7, 14, or 21 days. Hens fasted and hens fed diets with 10,000 ppm ZnO at the start of the experiment ceased production in significantly less time (4.6 to 6 days) than hens fed 5,000 ppm ZnO (14.3 to 14.9 days); however, days to return to 50% production from the start of the experiment did not differ among treatments. Feed consumption and feed cost per hen day during molt were lowest (P less than .05) in the fasted hens.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Heterochromatin associated with active versus inactive centromeres of mouse replicates at different times.

A subline of mouse L-cells carries a dicentric chromosome in which one centromere always separates prematurely. This centromere is not involved in the dynamics of chromosome migration and is considered inactive. By use of anti-BRdU antibody binding to BRdU-treated chromosomes it is shown that the pericentric constitutive heterochromatin associated with the prematurely separating centromere replicates earlier than its counterpart associated with the active centromere and even before several euchromatic regions in the genome. These results point to a possible mechanism by which dicentric chromosomes segregate equationally.

Animals↗
PubMed1994

Polydnavirus of the parasitic wasp Chelonus inanitus (Braconidae): characterization, genome organization and time point of replication.

Ultrastructural analysis of the polydnavirus of the braconid wasp Chelonus inanitus revealed that virions consist of one cylindrical nucleocapsid enveloped by a single unit membrane. Nucleocapsids have a constant diameter of 33.7 +/- 1.4 nm and a variable length of between 8 and 46 nm. Spreading of viral DNA showed that the genome consists of circular dsDNA molecules of variable sizes and measurement of the contour lengths indicated sizes of between 7 and 31 kbp. When virions were exposed to osmotic shock conditions to release the DNA, only one circular molecule was released per particle suggesting that the various DNA molecules are singly encapsidated in this bracovirus. The viral genome was seen to consist of at least 10 different segments and the aggregate genome size is in the order of 200 kbp. By partial digestion of viral DNA with HindIII or EcoRI in the presence of ethidium bromide and subsequent ligation with HindIII-cut pSP65 or EcoRI-cut pSP64 and transfection into Escherichia coli, libraries of 103 HindIII and 23 EcoRI clones were obtained. Southern blots revealed that complete and unrearranged segments were cloned with this approach, and restriction maps for five segments were obtained. Part of a 16.8 kbp segment was sequenced, found to be AT-rich (73%) and to contain six copies of a 17 bp repeated sequence. The development of the female reproductive tract in the course of pupal-adult development of the wasp was investigated and seen to be strictly correlated with the pigmentation pattern. By the use of a semiquantitative PCR, replication of viral DNA was observed to initiate at a specific stage of pupal-adult development.

Animals↗
PubMed1984

Performance, ruminal and serum characteristics of steers fed lasalocid on pasture.

Seventy-two growing steers were used in a 126-d study to determine the influence of varying levels of lasalocid on performance, ruminal and serum characteristics of animals grazing pasture. Treatments consisted of: 1) control; 2) 200 mg lasalocid/d and 3) 300 mg lasalocid/d. Each treatment was replicated three times and each replicate of eight steers was maintained on 3.0 ha of pasture. Pastures consisted of a mixture of tall fescue, orchard grass and ladino clover. In addition to pasture, each replicate of steers was group fed ground corn at a rate of .91 kg X head-1 X d-1 with the lasalocid incorporated into the grain. Average daily gains were .50, .60 and .57 kg, respectively, for steers on the control, and for the 200 and 300 mg lasalocid treatments, which differed (P less than .05) from controls. Ruminal acetate (mol/100 mol) was lower (P less than .05) in steers fed lasalocid at 28 d, but similar for all treatments at 56 and 112 d. Molar proportion of propionate was higher (P less than .05) and butyrate and valerate were lower (P less than .10) in rumen fluid of steers receiving 200 or 300 mg/d of lasalocid. Plasma glucose concentrations were similar for controls and steers receiving 200 mg lasalocid/d, but higher (P less than .05) in steers fed 300 mg lasalocid/d. Serum Mg concentrations were lower (P less than .01) in steers receiving lasalocid. Potassium concentrations in serum were slightly lower (P less than .01) in animals fed lasalocid at 112 d, but not at 28 or 56 d.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Origins of replication and gene regulation.

Eukaryotic chromosomes appear to consist of many replicons, the time of replication of which is probably controlled by specific origins. However, plasmids without specific eukaryotic origins may also replicate in some cells when injected into nuclei or transferred during transformation. The efficiency and the mechanisms of their initiation are still uncertain. A number of reports are cited which indicate that natural eukaryotic DNAs initiate their replication from specific origins. The nature of these origins are known in only a few instances and no general conclusions can yet be given about the nucleotide sequences involved. Short dispersed repeats of the Alu type appear to function as origins since they enhance the efficiency of replication of vector plasmids in Xenopus eggs. Certain sequences from a variety of eukaryotic DNAs also enhance the replicative potential of plasmids in yeast cells. The common features of such initiators or enhancers is uncertain. If dispersed repeats are origins in mammalian chromosomes, the number appears to be excessive. Either only a subset are functional, or the functional ones are only suborigins in larger replicons in which master origins (not yet isolated) function in the regulation of the timing of replication. Evidence is cited which indicates that the regulation of the time of replication of a gene or gene cluster is part of a regulatory system that makes the DNA available for transcription or leaves it in an inactive state. About one-half the DNA in mammalian cells is replicated in the first half of S phase (SE). After a brief pause in mid-S phase, the remainder of the DNA is replicated in what is designated late S (SL). The fractions replicated in SE and SL may vary in other phylogenetic groups, but wherever division of differentiated cells occurs such fractions are likely to be found. The following hypothesis is proposed. The DNA replicated in SL is suppressed in transcription, if it has the appropriate promoter regions, because the newly replicated DNA is complexed with proteins that suppress transcription. These proteins are only available during SL. Those genes replicated in SE are complexed with a different set of proteins which leave the promoter regions open for transcription when the appropriate regulatory molecules are available. In this way an inactive state or potentially active state can be transmitted from one cell generation to the next. Evidence is cited which indicates that genes which are active in all cells at some stage in the cell cycle are replicated in SE.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1973

Control of F'lac replication in Escherichia coli B-r.

The timing of replication of an F'lac plasmid during the division cycle of Escherichia coli B/r lac(-)/F'lac was examined in relation to the timing of initiation of chromosome replication. This was accomplished by measuring the induction of beta-galactosidase and the incorporation of radioactive thymidine into cells at different ages in cultures growing exponentially at various rates. In cells growing with interdivision times of 27, 36, and 55 min, the F'lac replicated at various stages in the division cycle but always at approximately the same time as initiation of chromosome replication. In cells growing with an interdivision time of 85 min, the F'lac episome replicated midway through the division cycle, whereas chromosome replication initiated at the start of the cycle. Measurements of absorbance at 450 nm per cell suggested that the F'lac replicated when the cells reached a mass which was a constant multiple of the number of episomes per cell at each growth rate. In contrast, the mass per cell at initiation of chromosome replication in cells with an 85-min interdivision time was significantly lower than this constant value. A possible explanation for the apparent coupling between F'lac replication and initiation of chromosome replication at the higher growth rates, and the lack of coupling at the lowest growth rate, is discussed.

Carbon Isotopes↗
PubMed1990

Time-delay discrimination training: replication with different stimuli and different populations.

Two time-delay conditions for teaching complex visual discriminations to normal preschoolers and children with mild and moderate intellectual handicaps were compared. One condition involved spatially separating the distinctive components from the redundant parts of both stimuli (multiple dynamic distinctive-feature prompts). The other condition involved adding a colored field to the correct stimulus (single static nondistinctive-feature prompt). The effect of the latter condition was assessed with unlearned and learned tasks. The study consisted of four experiments. In one experiment, children were also required to use the prompts for self-monitoring responses given before prompting had occurred. The results indicated that for all populations and stimuli (a) time delay of multiple dynamic distinctive-feature prompts consistently produced learning, and (b) time delay of the single static nondistinctive-feature prompt almost never produced learning and frequently led to a complete loss of discriminative performance on previously learned tasks. The resistance to disruption was a function of the training history (i.e., with or without time delay) and IQ level. Self-monitoring increased the efficacy of time delay when multiple dynamic distinctive-feature prompts were used but not when the single static nondistinctive-feature prompt was used.

Adolescent↗
PubMed1984

The beta-major and beta-minor globin genes in murine erythroleukemia cells replicate during the same early interval of the S phase.

The time of replication in S phase was determined for the 7.3 kb EcoRI segment containing the beta-major globin gene and the 14 kb EcoRI segment containing the beta-minor globin gene in a murine Friend erythroleukemia virus transformed (MEL) cell line. Cells were obtained from different intervals of S phase by centrifugal elutriation to avoid artifacts of chemical synchronization. Newly synthesized DNA from different parts of S phase were obtained by isolation of 5-bromouracil (BU) labelled DNA from these cells. The BU-DNA synthesized during four different intervals of S was transferred to diazobenzyloxymethyl (DBM) paper and hybridized with a beta-globin cDNA probe. Quantitation showed that both beta-globin segments were replicated in the first quarter of the S phase with no significant difference in their time of replication in this MEL cell line.

Animals↗
PubMed1992

Escherichia coli cells lacking methylation-blocking factor (leucine-responsive regulatory protein) have precise timing of initiation of DNA replication in the cell cycle.

A protein that is required for specific methylation inhibition of two GATC sites in the papBA pilin promoter region, known as methylation-blocking factor (Mbf) and recently shown to be identical to the leucine-responsive regulatory protein (Lrp), is not responsible for the delayed methylation at oriC implicated in an eclipse period following initiation of DNA replication. Cells containing a transposon mutation within the mbf (lrp) gene initiate DNA replication at the correct time during the cell cycle, whereas cells with increased amounts of the Dam methyltransferase initiate DNA replication randomly throughout the cell cycle.

Bacterial Proteins↗
PubMed1992

The efficiency and timing of plasmid DNA replication in Xenopus eggs: correlations to the extent of prior chromatin assembly.

Injection of the circular plasmid FV1 (derived from type I bovine papilloma virus) into Xenopus eggs before the start of the first cell cycle dramatically increases the efficiency of plasmid replication once eggs are chemically activated. We call this the preloading effect and report kinetic and quantitative characterization of this phenomenon here. The timing and the amount of FV1 synthesis were measured by both BrdUTP density labelling and an optimized method of selective enzymatic digestion of replicated and unreplicated molecules using the three methyladenosine-sensitive isoschizomers, DpnI, MboI and Sau3a. DpnI in 100 mM NaCl proved particularly useful for distinguishing and quantitating unreplicated, once-replicated, and repeatedly replicated molecules accumulated over several cell cycles. Our results reveal that both the amount of DNA replicated and the timing of synthesis during the first S-phase correlate with the length of the preloading period. Longer preloading leads to larger amounts of DNA being replicated sooner. In fact, up to 30-50% of 1 ng injected plasmid can replicate in a semiconservative cell cycle-dependent manner during the first S-phase. But such high levels of synthesis during the first cell cycle appear to limit the egg's ability to rereplicate this material in subsequent cell cycles. The preloading effect does not depend on synthesis of either viral or egg proteins, but does appear to correlate with the extent of plasmid assembly into chromatin before the start of the cell cycle. We postulate that each plasmid molecule must achieve a critical degree of chromatin assembly before it can proceed along the replication pathway. These observations illuminate some of the difficulties inherent in building a vector for gene insertion into Xenopus embryos, but also suggest an experimental strategy toward this aim.

Animals↗
PubMed1990

Centromere separation. Early replication of repetitive DNA associated with inactive centromeres.

Four types of stable dicentric and one octacentric chromosomes from mouse brain tumor cells and L-929 cells were analyzed for the timing of replication of repetitive deoxyribonucleic acid (DNA) located in the centric and pericentric regions associated with active versus inactive centromeres. The repetitive DNA present in the heterochromatin blocks of inactive centromeres replicates much earlier than similar DNA associated with the active centromeres. The former appears to replicate during early to mid S when several euchromatic segments are still replicating. There seems to be little or no overlap in the timing of replication of the repetitive DNA present in the vicinity of prematurely separating centromeres (which are accessory and nonfunctional) and those that separate at meta-anaphase junction (which are the functional centromeres). In the absence of any information about the mechanism(s) controlling initiation and completion of DNA synthesis in the two types of heterochromatic blocks, the differential timing of replication of the DNA with similar base composition remains an enigma.

Animals↗
PubMed1992

Adaptation to juvenile rheumatic disease: a controlled evaluation of functional disability with a one-year follow-up.

Compared the adaptation of 165 patients with juvenile rheumatic disease (JRD) to that of their healthy siblings. Patients were divided into those with mild functional disability and those with moderate/severe disability. Adaptation in several domains was assessed by parents and children on two occasions 1 year apart. The adjustment difficulties of the JRD children were limited primarily to social functioning but appeared also in the psychological and family problems domains. Compared to "mild" patients, "moderate/severe" patients had more adjustment difficulties; in some areas, mild patients functioned as well as their healthy siblings. Some Time 1 differences were replicated at Time 2. The results help to delineate (a) the specific domains in which children with chronic disease have adjustment difficulties and (b) the factors that put children at risk for developing adjustment problems.

Activities of Daily Living↗