Translational control in lysates of Drosophila melanogaster cells.

Abstract

Cell-free protein-synthesizing systems made from D. melanogaster cells were used to study the translational control induced in these cells by heat shock. Lysates of normally growing cells, termed 25.degree. C cells, translate both normal and heat shock mRNAs. Lysates of cells heat shocked at 36.degree. C for 1 h, termed 36.degree. C cells, translate preferentially heat-shock mRNAs and a few 25.degree. C cell mRNAs. Both lysates appear to reproduce the control displayed in vivo. Both lysates are optimally active at 28.degree. C, and all translations are done at that temperature, demonstrating that, once established, the discrimination system does not require heat-shock temperature for its activity. Addition of crude ribosome fractions from 25.degree. C cell lysates to lysates from heat-shocked cells rescues translation of 25.degree. C cell mRNA, which suggests that the discriminating elements are associated with ribosomes. Neither the heat-shock crude ribosome supplements nor the soluble fractions have any effect on either lysate. The experiments also show that RNA selection is determined by some feature of the RNA structure that is insensitive to protease digestion and phenol/chloroform extraction. The essential structural feature may not be unique to Drosophila mRNAs because the Drosophila lysate is capable of discriminating among mRNAs from other organisms.