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111.
Alan P. Merriam 《American anthropologist》1967,69(6):785-786
112.
Ribosomal protein insufficiency and the minute syndrome in Drosophila: a dose-response relationship.
Minutes comprise > 50 phenotypically similar mutations scattered throughout the genome of Drosophila, many of which are identified as mutations in ribosomal protein (rp) genes. Common traits of the Minute phenotype are short and thin bristles, slow development, and recessive lethality. By mobilizing a P element inserted in the 5'' UTR of M(3)95A, the gene encoding ribosomal protein S3 (RPS3), we have generated two homozygous viable heteroalleles that are partial revertants with respect to the Minute phenotype. Molecular characterization revealed both alleles to be imprecise excisions, leaving 40 and 110 bp, respectively, at the P-element insertion site. The weaker allele (40 bp insert) is associated with a approximately 15% decrease in RPS3 mRNA abundance and displays a moderate Minute phenotype. In the stronger allele (110 bp insert) RPS3 mRNA levels are reduced by approximately 60%, resulting in an extreme Minute phenotype that includes many morphological abnormalities as well as sterility in both males and females due to disruption of early gametogenesis. The results show that there is a correlation between reduced RPS3 mRNA levels and the severity of the Minute phenotype, in which faulty differentiation of somatic tissues and arrest of gametogenesis represent the extreme case. That heteroalleles in M(3)95A can mimic the phenotypic variations that exist between different Minute/rp-gene mutations strongly suggests that all phenotypes primarily are caused by reductions in maximum protein synthesis rates, but that the sensitivity for reduced levels of the individual rp-gene products is different. 相似文献
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Jeffrey L. Merriam William H. McDowell Jennifer L. Tank Wil M. Wollheim Chelsea L. Crenshaw & Sherri L. Johnson 《Freshwater Biology》2002,47(1):143-160
1. This study was part of the Lotic Intersite Nitrogen eXperiment (LINX); a series of identical 15NH4 tracer additions to streams throughout North America. 15NH4Cl was added at tracer levels to a Puerto Rican stream for 42 days. Throughout the addition, and for several weeks afterwards, samples were collected to determine the uptake, retention and transformation pathways of nitrogen in the stream. 2. Ammonium uptake was very rapid. Nitrification was immediate, and was a very significant transformation pathway, accounting for over 50% of total NH4 uptake. The large fraction of NH4 uptake accounted for by nitrification (a process that provides energy to the microbes involved) suggests that energy limitation of net primary production, rather than N limitation, drives N dynamics in this stream. 3. There was a slightly increased 15N label in dissolved organic nitrogen (DON) the day after the 15NH4 addition was stopped. This DO15N was < 0.02% of DON concentration in the stream water at the time, suggesting that nearly all of the DON found in‐stream is allochthonous, or that in‐stream DON production is very slow. 4. Leptophlebiidae and Atya appear to be selectively feeding or selectively assimilating a very highly labelled fraction of the epilithon, as the label found in the consumers became much higher than the label found in the food source. 5. A large spate (>20‐fold increase in discharge) surprisingly removed only 37% of in‐stream fine benthic organic matter (FBOM), leaves and epilithon. The fraction that was washed out travelled downstream a long distance (>220 m) or was washed onto the stream banks. 6. While uptake of 15NH4 was very rapid, retention was low. Quebrada Bisley retained only 17.9% of the added 15N after 42 days of 15N addition. Most of this was in FBOM and epilithon. Turnover rates for these pools were about 3 weeks. The short turnover times of the primary retention pools suggest that long‐term retention (>1 month) is minimal, and is probably the result of N incorporation into shrimp biomass, which accounted for < 1% of the added 15N. 相似文献
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Purified chloroplast tRNAs were isolated fromPisum sativum leaves and radioactively labeled at their 3′ end using tRNA nucleotidyl transferase and α32P-labeled CTP. Pea ctDNA was fragmented using a number of restriction endonucleases and hybridized with thein vitro labeled chloroplast tRNAs by DNA transfer method. Genes for tRNAs have been found to be dispersed throughout the chloroplast
genome. A closer analysis of the several hybrid regions using recombinant DNA plasmids have shown that tRNA genes are localized
in the chloroplast genome in both single and multiple arrangements. Two dimensional gel electrophoresis of total ct tRNA have
identified 36 spots. All of them have been found to hybridize withPisum sativum ctDNA. Using recombinant clones, 30 of the tRNA spots have been mapped inPisum sativum ctDNA. 相似文献