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J E Garrett

Publications and source records attributed to J E Garrett.

61 records · Page 4Linked to original sources
PubMed1986

Tx1: a transposable element from Xenopus laevis with some unusual properties.

A family of transposable genetic elements in the genome of the frog, Xenopus laevis, is described. They are designated Tx1. Transposability of the elements was deduced by characterization of a chromosomal locus which is polymorphic for the presence or absence of a Tx1 element. Nucleotide sequence analysis suggested that Tx1 elements show target site specificity, as they are inserted at the pentanucleotide TTTAA in all four cases that were examined. The elements appear to have 19-base-pair (bp) inverted terminal repeats, and they are flanked by 4-bp target duplications (TTAA), although the possibility that they do not create target site duplications is discussed. Tx1 elements have several unusual characteristics: the central portion of each element is comprised of a variable number of two types of 393-bp repeating units; the rightmost 1,000 bp of the element contains separate regions potentially capable of forming bends, left-handed Z-form DNA, and alternative stem-loop structures. Comparisons among single frogs suggest that germ line transposition is relatively infrequent and that variations in numbers of internal repeats accumulate quite slowly at any locus.

Animals↗
PubMed1984

Isolated clusters of paired tandemly repeated sequences in the Xenopus laevis genome.

There exist in the Xenopus laevis genome clusters of tandemly repeated DNA sequences, consisting of two types of 393-base-pair repeating unit. Each such cluster contains several units of one of these paired tandem repeats (PTR-1), followed by several units of the other repeat (PTR-2). The number of repeats of each type is variable from cluster to cluster and averages about seven of each type per cluster. Every cluster has ca. 1,000 base pairs of common left flanking sequence (adjacent to the PTR-1 repeats) and 1,000 base pairs of common right flanking sequence (adjacent to the PTR-2 repeats). Beyond these common flanks, the DNA sequences are different in the eight cloned genomic fragments we have studied. Thus, the hundreds of PTR clusters in the genome are dispersed at apparently unrelated sites. Nucleotide sequences of representative PTR-1 and PTR-2 repeats are 64% homologous. These sequences do not reveal an obvious function. However, the related species X. mulleri and X. borealis have sequences homologous to PTR-1 and PTR-2, which show the same repeat lengths and genomic organization. This evolutionary conservation suggests positive selection for the clusters. Maintenance of these sequences at dispersed sites imposes constraints on possible mechanisms of concerted evolution.

Animals↗
PubMed1984

Influence of monensin on the performance of cattle.

Performance data on nearly 16,000 head of cattle that were used in trials to document effects of monensin on feedlot cattle were summarized. Cattle fed monensin-containing diets gained 1.6% faster, consumed 6.4% less feed and required 7.5% less feed/100 kg gain than cattle fed control diets. Monensin resulted in the greatest improvement in feed/gain at 2.9 Mcal metabolizable energy (ME)/kg diet dry matter (DM). Within the range of monensin concentrations used in the trials that were summarized (31.8 +/- 7.5 mg/kg DM), high monensin concentrations did not improve feed/gain over that obtained with lower concentrations. Carcass characteristics were not significantly influenced by monensin. Responses of cattle to monensin and implants were additive. Energy metabolism data suggested that monensin improved digestibility of DM, reduced fasting heat production and increased dietary net energy maintenance (NEm) values more than it increased net energy gain (NEg) values. Data showing the response of cattle to monensin when fed various dietary protein concentrations or sources of supplemental N suggested that monensin had a protein sparing effect. Monensin has also been shown to reduce lactic acid production, aid in the control of coccidia and bloat and to be toxic to face and horn fly larva in feces of monensin-fed cattle. In pasture trials, monensin improved daily gains. When fed to beef cows, monensin reduced amounts of feed required to maintain cow weight.

Acidosis↗
PubMed1980

Elongating nerve fibers are guided by a pathway of material released from embryonic nonneuronal cells.

Dissociated parasympathetic neurons rapidly initiate neurite outgrowth when exposed to culture medium previously conditioned by the growth of embryonic heart cells. The inducer of neurite outgrowth in the conditioned medium is a substratum-conditioning factor; that is, it does not act in a soluble form, but acts only when bound to the nerve cell culture substratum. When a sharp border is created between a region of the substratum coated with this factor and a region coated with unconditioned medium, neurites fail to cross this border; rather, they change their direction of outgrowth so as to remain on the conditioned substratum. Thus, long after the initiation of outgrowthhas been induced, elongating neurites continue to respond to the substratum-conditioning factor in a manner that allows their outgrowth to be channeled along a pathway of this neurotropic substratum-associated material.

Animals↗