Starved Tetrahymena thermophila Cells That Are Unable to Mount an Effective Heat Shock Response Selectively Degrade Their rRNA

Abstract

Tetrahymena thermophila cells that had been shifted from log growth to a non-nutrient medium (60 mM Tris) were unable, during the first few hours of starvation, to mount a successful heat shock response and were killed by what should normally have been a nonlethal heat shock. An examination of the protein synthetic response of these short-starved cells during heat shock revealed that whereas they were able to initiate the synthesis of heat shock proteins, it was at a much reduced rate relative to controls and they quickly lost all capacity to synthesize any proteins. Certain pretreatments of cells, including a prior heat shock, abolished the heat shock inviability of these starved cells. Also, if cells were transferred to 10 mM Tris rather than 60 mM Tris, they were not killed by the same heat treatment. We found no abnormalities in either heat shock or non-heat shock mRNA metabolism in starved cells unable to survive a sublethal heat shock when compared with the response of those cells which can survive such a treatment. However, selective rRNA degradation occurred in the nonsurviving cells during the heat shock and this presumably accounted for their inviability. A prior heat shock administered to growing cells not only immunized them against the lethality of a heat shock while starved, but also prevented rRNA degradation from occurring.

A Highly Evolutionarily Conserved Mitochondrial Protein Is Structurally Related to the Protein Encoded by the Escherichia coli groEL Gene

“…Preparation of mitochondrial and total protein samples from other organisms. T. thermophila CU355 (II) was grown at 30°C on a gyratory shaker in 1% Difco Proteose Peptone supplemented with 0.003% Sequestrene (CIBA-GEIGY Corp.) as previously described (18,19). The preparation of mitochondria from T. thermophila has been described previously (34).…”

“…The protein concentration in each sample was determined by the Bio-Rad protein assay system. The procedure for the one-dimensional separation of proteins by SDS-PAGE has been described previously (18,19). Staining of gels with Coomassie brilliant blue R has been described previously (18).…”

“…The procedure for the one-dimensional separation of proteins by SDS-PAGE has been described previously (18,19). Staining of gels with Coomassie brilliant blue R has been described previously (18). Silver staining was done by the procedure of Wray et al (50).…”

“…In Tetrahymena thermophila, shifting cells to 37 through 41°C induces the selective synthesis of a specific array of HSPs (16,18,19,33,49). Recently, we purified and characterized a minor member of this set of proteins.…”

Induction of Acquired Thermotolerance in Tetrahymena thermophila: Effects of Protein Synthesis Inhibitors

“…(i) Northern transfers. RNA denatured with glyoxal by the method of McMaster and Carmichael (25) was run on 1% agarose gels as previously described (15).…”