Abstract
CELL BIOLOGY When the outer membrane of a eukaryotic cell is damaged (for instance, by ripping), a calcium-dependent repair process involving the fusion of lysosomal membrane with the plasma membrane is set in motion. Bacterial toxins can also perforate the plasma membrane, but do so by forming protein-delimited holes. How does a cell repair this kind of puncture? Idone et al . show that, in addition to patching the portion of damaged membrane using exocytosis, the cell arranges for the removal of the perforated areas from the cell surface via a process of calcium-stimulated endocytosis. Treating cells with the bacterial toxin streptolysin, which forms stable membrane-embedded pores, induced a calcium- and sterol-dependent form of endocytosis that cleared the pores from the plasma membrane, leading to the rapid (in less than a minute) resealing of the cell; independently stimulating endocytosis also promoted membrane repair. Thus, cells use two mechanistically linked pathways, which are both stimulated by high levels of extracellular calcium, to activate membrane repair after physical injury. — SMH J. Cell Biol . 180 , 905 (2008).
Highlights
Mammalian genomes are packed to overflowing with a menagerie of repetitive DNA elements, many of which are derived from defunct transposons
A clue to the basis for the persistence of these apparently “parasitic” DNA regions in the mouse comes from the observation that the noncoding RNA transcribed from B2 SINEs in response to heat shock can act to repress specific protein-coding genes by binding to and repressing RNA polymerase II
Mariner et al show that human Alu ncRNA, like mouse B2 ncRNA, can repress specific genes in response to heat shock, and that, like B2 RNA, it achieves this by binding to the RNA polymerase II (pol II) pre-initiation complex, probably preventing appropriate interaction with promoter DNA
Summary
Many plant roots establish a symbiotic relationship with either bacteria or fungi in order to gain access to nutrients, such as fixed nitrogen or phosphate, respectively. Markmann et al and Gherbi et al have investigated the evolution of symbiotic relationships between plants and Intimate associations between plants and bacteria and fungi. Additional investigation revealed that the protein is highly conserved in its ability to mediate these interactions and that this protein does not mediate the exclusive host/symbiont interactions found among species. Three structural SYMRK versions exist among plants with different functional capabilities in the development of root/symbiont interactions, providing an evolutionary hypothesis for the origin of the highly derived nodules in legumes and their close relatives.
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