A component of the interphase cytoskeleton is cyclically recruited into spindle poles during mitosis

During the transition from interphase to mitosis, proteins are recruited into forming spindle poles [Leslie, Cell Motil. Cytoskeleton 16:225-228, 1990]. Antibodies which recognize these recruited components clearly label spindle poles during mitosis but the location and character of such proteins during interphase remain a mystery. Competition assays using an antibody to a recruited spindle pole protein show that in its disperse form the spindle pole protein is a highly insoluble component of the cytoskeleton which is dispersed to such an extent during interphase that it is difficult to identify by immunolocalization. The function of recruited spindle pole proteins is unknown but the aggregation/dispersion cycle and the antigen are highly conserved, appearing in sea urchin embryos and tissue culture cells.     

Nuclear genes coding for four subunits of the yeast ubiquinol-cytochrome c reductase complex are present in single copies in the haploid genome and at least two of these are located on different chromosomes

Summary Genes coding for the 40 kilodaltons (kDa), 17-kDa, 14-kDa and 11-kDa subunits of the ubiquinol-cytochrome c reductase in yeast are present in single copies in the haploid genome. We have mapped each gene to a unique genomic environment and demonstrate that integration of cloned segments into nuclear DNA by homologous crossing-over with the endogenous gene results in the replacement of the corresponding chromosomal restriction fragment by fragments of predicted sizes. Chromosomal mapping, carried out by the procedure of Falco and Botstein 1983, indicates that the gene for the 17-kDa subunit lies on chromosome VI and that for the 11-kDa subunit on chromosome XII.     

Agrobacterium-mediated inoculation of plants with tomato golden mosaic virus DNAs

We have adapted the agroinfection procedure of Grimsley and co-workers [4,5] to develop a simple, efficient, reproducible infectivity assay for the insect-transmitted, split-genome geminivirus, tomato golden mosaic virus (TGMV). Agrobacterium T-DNA vectors provide efficient delivery of both components of TGMV when used in mixed inoculation of wild-type host plants. A greater increase in infection efficiency can be obtained by Agrobacterium delivery of the TGMV A component to permissive transgenic plants. These permissive plants contain multiple tandem copies of the B component integrated into the host genome. An inoculum containing as few as 2000 Agrobacterium cells can produce 100% infection under these conditions. Further, our results show that there is a marked effect of the configuration of the TGMV A components within the T-DNA vector on time of symptom development. We have also found that transgenic plants carrying tandem copies of the A component do not complement the B component. Possible mechanisms to explain these results and the potential use of this system to further study the functions of the geminivirus components in infection are discussed.     

Oxygen-Poor Microzones as Potential Sites of Microbial N2 Fixation in Nitrogen-Depleted Aerobic Marine Waters

The nitrogen-deficient coastal waters of North Carolina contain suspended bacteria potentially able to fix N₂. Bioassays aimed at identifying environmental factors controlling the development and proliferation of N₂ fixation showed that dissolved organic carbon (as simple sugars and sugar alcohols) and particulate organic carbon (derived from Spartina alterniflora) additions elicited and enhanced N₂ fixation (nitrogenase activity) in these waters. Nitrogenase activity occurred in samples containing flocculent, mucilage-covered bacterial aggregates. Cyanobacterium-bacterium aggregates also revealed N₂ fixation. In all cases bacterial N₂ fixation occurred in association with surficial microenvironments or microzones. Since nitrogenase is oxygen labile, we hypothesized that the aggregates themselves protected their constituent microbes from O₂. Microelectrode O₂ profiles revealed that aggregates had lower internal O₂ tensions than surrounding waters. Tetrazolium salt (2,3,5-triphenyl-3-tetrazolium chloride) reduction revealed that patchy zones existed both within microbes and extracellularly in the mucilage surrounding microbes where free O₂ was excluded. Triphenyltetrazolium chloride reduction also strongly inhibited nitrogenase activity. These findings suggest that N₂ fixation is mediated by the availability of the appropriate types of reduced microzones. Organic carbon enrichment appears to serve as an energy and structural source for aggregate formation, both of which were required for eliciting N₂ fixation responses of these waters.