A differential effect of the incubation temperature on the inhibition of RNA synthesis by DRB in cells of Drosophila hydei

An Important Role for RPRD1B in the Heat Shock Response

During the heat shock response (HSR), heat shock factor (HSF1 in mammals) binds to target gene promoters, resulting in increased expression of heat shock proteins that help maintain protein homeostasis and ensure cell survival. Besides HSF1, only a relatively few transcription factors with a specific role in ensuring correctly regulated gene expression during the HSR have been described. Here, we use proteomic and genomic (CRISPR) screening to identify a role for RPRD1B in the response to heat shock. Indeed, cells depleted for RPRD1B are heat shock sensitive and show decreased expression of key heat shock proteins (HSPs). These results add to our understanding of the connection between basic gene expression mechanisms and the HSR.

DRB resistance in Chinese hamster and human cells: genetic and biochemical characteristics of the selection system

Stable mutants resistant to the nucleoside analog 5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole (DRB), which interferes with RNA synthesis, have been selected in Chinese hamster ovary (CHO) and human diploid fibroblasts. In CHO cells, upon treatment with the mutagen ethyl-methane sulfonate (EMS), a linear dose--response between the concentration of mutagen and the frequency of DrbR mutants was observed in the range of 20--300 micrograms/ml. The selection system did not show cell density or cross-feeding effects, and the optimal expression time following mutagenesis was found to be 2--3 days for CHO cells and 5--6 days for human fibroblasts. The DrbR mutation behaved codominantly in DrbR x DrbS hybrids. Addition of DRB affected nucleoside uptake to a similar extent in both wild-type and mutant cells, indicating that the drug was able to enter the mutant cells. The failure of DrbR mutants to show any cross-resistance to other toxic nucleoside analogs examined suggests that the action of DRB does not involve the initial phosphorylation step. DRB addition did not cause any marked inhibition of either RNA polymerase I or RNA polymerase II activity from both wild-type and mutant cells in vitro, indicating that its effect on RNA synthesis may be indirect.

The products of the "heat-shock" loci of Drosophila hydei. Correlation between locus 2-36A and the 70,000 MW "heat-shock" peptide

Antibody was raised against total Drosophila hydei embryonic cellular protein with a molecular weight between 65,000 and 70,000 dalton. This antiserum reacted with the 70,000 MW "heat-shock" peptide found in "S labelled cell extracts of "heat-shocked" D. hydei tissue culture cells or salivary glands.--The antibody was coupled to Sepharose 4B and this material was used to absorb polysomes obtained from tissue culture cells incubated at 37 degrees C in the presence of tritiated RNA precursors. The relative concentrations of various RNA species complementary to the "heat-shock" loci 2-32A, 2-36A, and 2-48C in either bound, non-bound, or total polysomal material was then determined by in situ hybridization. The RNA species complementary to locus 2-36A was found to be enriched in the bound polysomal material.