Protein Synthesis and Breakdown during Heat Shock of Cultured Pear (Pyrus communis L.) Cells |
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| Authors: | Ferguson I B Lurie S Bowen J H |
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| Affiliation: | Horticulture and Food Research Institute of New Zealand, Private Bag 92 169, Auckland, New Zealand (I.B.F., J.H.B). |
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| Abstract: | Cultured pear (Pyrus communis L. cv Passe Crassane) cells were subjected to temperatures of 39, 42, and 45deg]C. Heat-shock protein (hsp) synthesis was greater at 30deg]C than at temperatures above 40deg]C and continued for up to 8 h. Both cellular uptake of radiolabeled methionine and total protein synthesis were progressively lower as the temperature was increased. Polysome levels decreased immediately when cells were placed at 39 or 42deg]C, although at 39deg]C the levels began to recover after 1 h. In cells from both temperatures, reassembly occurred after transfer of cells to 25deg]C Four heat-shock-related mRNAsmdash]hsp17, hsp70, and those of two ubiquitin genesmdash]all showed greatest abundance at 39deg]C and decreased at higher temperatures. Protein degradation increased with time at 42 and 45deg]C, but at 39deg]C it increased for the first 2 h and then decreased. In the presence of cycloheximide, which prevented hsp synthesis, protein degradation at 39deg]C was as great as that at 45deg]C in the absence of cycloheximide. The data suggest that hsps may have a role in protecting proteins from degradation at the permissive temperature of 39deg]C. At temperatures high enough to inhibit hsp synthesis, protein degradation was enhanced. Although ubiquitin may play a role in specific protein degradation, it does not appear to be involved in increased protein degradation occurring above 40deg]C. |
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