Abstract. Striated muscle contraction is elicited by the release of stored calcium ions through ryanodine receptor channels in the sarcoplasmic reticulum, ryr-1 is a C. elegans ryanodine receptor homologue that is expressed in body-wall muscle cells used for locomotion.Using genetic methods, we show that ryr-1 is the previously identified locus uric-68. First, transposon-induced deletions within ryr-1 are alleles of unc-68. Second, transformation of unc-68 mutants with ryr-1 genomic DNA results in rescue of the Unc phenotype, unc-68 mutants move poorly, exhibiting an incomplete flaccid paralysis, yet have normal muscle ultrastructure. The mutants are insensitive to the paralytic effects of ryanodine, and lack detectable ryanodine-binding activity. The Unc-68 phenotype suggests that ryanodine receptors are not essential for excitation-contraction coupling in nematodes, but act to amplify a (calcium) signal that is sufficient for contraction.

Maryon EB, Molloy SA, Kaplan JH. Cellular glutathione plays a key role in copper uptake mediated by human copper transporter 1.

Linear DNA injected into Xenopus laevis oocyte nuclei recombines with high efficiency if homologous sequences are present at overlapping molecular ends. We found that injected linear DNA was degraded by a 5'-*3' strand-specific exonuclease activity during incubation in the oocyte nucleus to leave a heterogeneous population of 3'-tailed molecules. Decreasing the concentration of DNA injected increased the heterogeneity and the average rate of degradation. The 3' tails created were relatively stable; among molecules persisting after overnight incubation, many had 3' tails intact to within 10 bases of the original ends. DNA molecules that were efficient substrates for homologous recombination in oocytes were also partially degraded, leaving 3' tails. We found no evidence for other potent nuclease activities. If molecules with recessed 3'-OH ends were injected, endogenous polymerase efficiently resynthesized complementary strands before degradation of the 5' tails occurred. 3'-tailed molecules are plausible intermediates in the initiation of homologous recombination events in Xenopus oocyte nuclei.Studies on a variety of organisms have shown a correlation between double-strand breaks in DNA and increased levels of homologous recombination (16,33,35,39). When introduced into cells, linear DNA is generally more efficient at recombination than circular DNA, and in most situations recombination events are focused near the ends of linear molecules. Double-strand breaks made in vivo can also stimulate recombination events at the site of the break (16, 39).Several models have been proposed for the initiation of eucaryotic homologous recombination events by DNA duplex ends. Typically, these start with degradation at the ends by hypothetical strand-specific exonucleases, leaving molecules with single-stranded tails (22,30,38). There is genetic and biochemical evidence in procaryotes for exonuclease activity in end-initiated recombination events. Genes known to encode strand-specific exonucleases are required for certain bacteriophage and bacterial recombination pathways in which recombination events are elevated near ends (32,39). Furthermore, the bacterial RecA protein can interact in vitro with DNA molecules having single-stranded tails and catalyze the invasion of homologous duplex DNA, creating crossed-strand recombination intermediates (41). Proteins from a variety of organisms have been shown to have analogous strand transfer activities (13,(17)(18)(19)25). It has not been proven, however, that DNA molecules which have undergone exonucleolytic degradation initiate procaryotic recombination events in vivo, nor have such molecules been physically isolated.Little genetic or biochemical evidence exists for the involvement of specific exonucleases in eucaryotic homologous recombination, but two laboratories have recently identified probable physical intermediates of recombination events initiated by double-strand breaks in Saccharomyces cerevisiae (16,36 cules had undergone strand-specific exonucleolytic degradation before ...

Cu is an essential micronutrient, and its role in an array of critical physiological processes is receiving increasing attention. Among these are wound healing, angiogenesis, protection against reactive oxygen species, neurotransmitter synthesis, modulation of normal cell and tumor growth, and many others. Free Cu is absent inside cells, and a network of proteins has evolved to deliver this essential, but potentially toxic, metal ion to its intracellular target sites following uptake. Although the total body content is low (∼100 mg), dysfunction of proteins involved in Cu homeostasis results in several well-characterized human disease states. The initial step in cellular Cu handling is its transport across the plasma membrane, a subject of study for only about the last 25 years. This review focuses on the initial step in Cu homeostasis, the properties of the major protein, hCTR1, that mediates Cu uptake, and the status of our understanding of this highly specialized transport system. Although a high-resolution structure of the protein is still lacking, an array of biochemical and biophysical studies have provided a picture of how hCTR1 mediates Cu(I) transport and how Cu is delivered to the proteins in the intracellular milieu. Recent studies provide evidence that the transporter also plays a key protective role in the regulation of cellular Cu via regulatory endocytosis, lowering its surface expression, in response to elevated Cu loads.