Adaptation mechanism of membrane lipids and its genetic control

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Temperature shift of Tetrahymena cells from 39 C to 15 C induced alterations in fatty acid composition of membrane phospholipids, a decrease in satureated palmitic acid and increases in unsaturated fatty acids such as -linoleinic and linoleic acids, causing its plasma membrane more fluid as inferred with ESR and freeze-fracture electron microscopy. Although low-temperature acclimation did not affect the viability of the cells, aggregation of monosome to form polysome was observed. Whether the increase in polysome content was derived from newly transcribed mRNA or not is to be clarified. Two dimensio- l gel electrophoretic analyses of microsomal proteins from low-temperature-shifted cells showed time-dependent increases in tubulin and some proteins which have lower apparent molecular masses than fatty acyl CoA-desaturase. Using two coding regions of rat liver stearyl-CoA desaturase cDNA, Southern blotting of Tetrahymena DNA was performed. Under low stringency of 35% formamide and 5xSSC, at 28 C for 24hr, EcoRI-digested DNA hybridized with one of the desaturase cDNA fragment. Furthermore, EcoRV- and BglII-digested DNA showed hybridizing bands of 2.6kb and 2.7kb, respectively, indicating a possibility of cloning Tetrahymena enzymes using rat-derived DNA as a probe.