The effect of culture conditions on the fluidity of mouse neuroblastoma membranes as estimated by spin label studies

Gas chromatography and spin labeling were used to estimate the composition and fluidity of the lipid acyl chains in intact cell membranes of mouse C1300 neuroblastoma. Neurite formation and an increase in the specific activity of acetylcholinesterase are induced in this cell line by the removal of serum from the culture medium for one day prior to harvesting the cells. The fatty acid composition of induced cells was not significantly different from that of the non-induced controls. Each of the three fatty acid spin labels used in this study indicate that the membranes of induced cells are slightly more fluid than the membranes of control cells. This difference in fluidity appears to be a result of a reduction in the progressive decrease in fluidity occurring during growth in serum. A four-fold reduction in cell viability had no effect on the measured bilayer fluidity. Thus the changes in fluidity appear to be due to the presence or absence of serum rather than to cell type, age, or viability.     

The FERONIA Receptor Kinase Maintains Cell-Wall Integrity during Salt Stress through Ca2+ Signaling

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Genetic Mapping of the BRCA1 Region on Chromosome 17q21

Chromosome 17q21 harbors a gene (BRCA1) associated with a hereditary form of breast cancer. As a step toward identification of this gene itself we developed a number of simple-sequence-repeat (SSR) markers for chromosome 17 and constructed a high-resolution genetic map of a 40-cM region around 17q21. As part of this effort we captured genotypes from five of the markers by using an ABI sequencing instrument and stored them in a locally developed database, as a step toward automated genotyping. In addition, YACs that physically link some of the SSR markers were identified. The results provided by this study should facilitate physical mapping of the BRCA1 region and isolation of the BRCA1 gene.     

Effect of Population Dynamics of Pseudomonas cepacia and Paecilomyces lilacinus on Colonization of Polyfoam Rooting Cubes by Rhizoctonia solani

Suspensions of Pseudomonas cepacia (strain 5.5B) and Paecilomyces lilacinus (isolate 6.2F) were applied to polyfoam rooting cubes for control of stem rot of poinsettia caused by Rhizoctonia solani. The populations of antagonists and colonization of rooting cubes by R. solani were monitored during a 3-week period. Colonization of cubes by R. solani was reduced in cubes treated with P. cepacia, but the population of P. cepacia decreased by as much as 97% during the test period. Increased colonization by R. solani was correlated with a decline in population of P. cepacia. P. lilacinus was more persistent than P. cepacia in cubes, with only a 21% reduction observed during the 3-week period. Colonization of the P. lilacinus-treated cubes by R. solani was significantly less than colonization of infested controls. No correlation existed between population of P. lilacinus and colonization of cubes by R. solani.     

A Sec62p-related component of the secretory protein translocon from Drosophila displays developmentally complex behavior.

The isolation and characterization of a Drosophila melanogaster gene (Dtrp1) that encodes a protein displaying the properties of both a structural and functional homolog of the yeast endoplasmic reticulum membrane-bound translocation protein Sec62p is reported. We show that Dtrp1 can not only rescue the lethality associated with a SEC62 gene knockout in yeast, but also complement the sec62-associated defective transport of a precursor polypeptide from the cytoplasm into the lumen of the endoplasmic reticulum. Expression of the Dtrp1 gene throughout Drosophila development is characterized by peaks in mid-embryo-genesis and mid-pupation, followed by a sustained period of mRNA accumulation in adults. The examination of male reproductive tissues showed a very high level of preferential expression of a 1.6 kb message, while a 2.2 kb message was confined almost exclusively to the non-reproductive tissues. Within the reproductive tract itself the 1.6 kb message was expressed in testes, ejaculatory duct and particularly strongly in the paragonial glands. Since these latter organs are specialized secretory tissues we suggest that the 1.6 kb message may encode a protein isoform that performs a unique, tissue-specific role in the protein translocation pathway. Such observations may indicate a hitherto unexpected diversity in components of the protein translocation pathway in respect to stage, tissue and, potentially, substrate specificity.     

Effect of ethanol on activity of the plasma-membrane ATPase in, and accumulation of glycine by, Saccharomyces cerevisiae

The pH optimum of the ATPase activity in plasma membranes from Saccharomyces cerevisiae NCYC 431 from 8 h cultures was around 6.5 and that in membranes from organisms from 16 h cultures near 6.0. The Km[ATP] of the enzyme was virtually unaffected by the age of the culture from which organisms were harvested, although the Vmax of the enzyme in membranes from organisms from 8 h cultures was higher than that for organisms from 16 h cultures. Ethanol non-competitively inhibited ATPase activity in membranes, although the inhibition constant for the enzyme from organisms from 8 h cultures was lower than that from organisms from 16 h cultures. Glycine accumulation by the general amino acid permease was non-competitively inhibited by ethanol. Inhibition constants were virtually the same for glycine uptake by deenergized organisms from 8 h and 16 h cultures, but under energized conditions the value was greater for organisms from 16 h rather than 8 h cultures. The data indicate that inhibition of plasma-membrane ATPase activity by ethanol could account, at least in part, for inhibition of glycine accumulation by ethanol.     

The effect of E. coli host strain on the consensus sequence of regions of the human L1 transposon.

We have used highly methylation tolerant host strains to clone hyper- and hypo-methylated genomic elements from different regions of the same family of long interspersed repetitive elements from human DNA, specifically the 1.8 kilobase (kb) and 1.2kb KpnI fragments from members of the L1 family of transposable elements in which respectively some 18% and 2.7% of cytosines are methylated in vivo in human spleen DNA. The consensus of the DNA sequences of the ends of 13 clones from the hypomethylated region of human L1 agreed exactly with the consensus derived previously from clones made using conventional host strains. However the sequences of 18 of our clones from the 5' end of the hypermethylated region differed significantly from the sequences of clones made using conventional hosts (P less than 0.0001). The 5' region of the 1.8kb L1 region is a CpG island which, in human somatic tissue, appears to be maintained in a highly methylated state, including methylation at sites other than CpG dinucleotides. The consensus sequence of this region also has features suggestive of a previously unrecognized open reading frame.