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691.
Specification of sites for polarized growth in Saccharomyces cerevisiae and the influence of external factors on site selection. 总被引:19,自引:1,他引:18 下载免费PDF全文
Many eucaryotic cell types exhibit polarized cell growth and polarized cell division at nonrandom sites. The sites of polarized growth were investigated in G1 arrested haploid Saccharomyces cerevisiae cells. When yeast cells are arrested during G1 either by treatment with alpha-factor or by shifting temperature-sensitive cdc28-1 cells to the restrictive temperature, the cells form a projection. Staining with Calcofluor reveals that in both cases the projection usually forms at axial sites (i.e., next to the previous bud scar); these are the same sites where bud formation is expected to occur. These results indicate that sites of polarized growth are specified before the end of G1. Sites of polarized growth can be influenced by external conditions. Cells grown to stationary phase and diluted into fresh medium preferentially select sites for polarized growth opposite the previous bud scar (i.e., distal sites). Incubation of cells in a mating mixture results in projection formation at nonaxial sites: presumably cells form projections toward their mating partner. These observations have important implications in understanding three aspects of cell polarity in yeast: 1) how yeast cell shape is influenced by growth conditions 2) how sites of polarized growth are chosen, and 3) the pathway by which polarity is affected and redirected during the mating process. 相似文献
692.
693.
M Safferling W Tichelaar G Kümmerle A Jouppila A Kuusinen K Kein?nen D R Madden 《Biochemistry》2001,40(46):13948-13953
We have expressed, purified, and characterized glutamate receptor ion channels (GluR) assembled as homomers of the subunit GluRB. For the first time, single-milligram quantities of biochemically homogeneous GluR have been obtained. The protein exhibits the expected pharmacological profile and a high specific activity for ligand binding. Density-gradient centrifugation reveals a uniform oligomeric assembly and a molecular mass suggesting that the channel is a tetramer. On the basis of electron microscopic images, the receptor appears to form an elongated structure that is visualized in several orientations. The molecular dimensions of the molecule are approximately 11 x 14 x 17 nm, and solvent-accessible features can be seen; these may contribute to formation of the ion-conducting pathway of the channel. The channel dimensions are consistent with an overall 2-fold symmetric assembly, suggesting that the tetrameric receptor may be a dimer of dimers. 相似文献
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695.
A study of the numbers of pulmonary endocrine cells per cm2 of section of lung obtained at combined heart-lung transplantation in 25 cases of plexogenic pulmonary arteriopathy demonstrated that the peptide which may become unduly prominent in pulmonary arterial disease is bombesin. The type of vascular disease in which bombesin becomes prominent is plexogenic pulmonary arteriopathy, be this primary or secondary to congenital heart disease. The increased prominence of bombesin appears to be related to the stage reached in the arteriopathy. Increased numbers of pulmonary endocrine cells are found in association with classic cellular plexiform lesions with narrow vascular channels. Their numbers are within normal limits when the plexiform lesions are mature with wide vascular channels and narrow intervening septa. The pulmonary endocrine cells are most prominent in the pre-plexiform stage when smooth muscle cells in the inner half of the media of the pulmonary artery show increased electron density, and migrate through gaps in the inner elastic lamina to reach the intima. Here they are transformed into myofibroblasts and proliferate. The migration of muscle cells may be related in some way to long-acting trophic factors released from the pulmonary endocrine cells into the surrounding tissues from which they reach the blood and hence the pulmonary arteries. 相似文献