STRESS RESPONSES IN CELL-CULTURES OF LOLIUM-TEMULENTUM .1. TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL CHANGES IN GENE-EXPRESSION DURING HEAT-SHOCK AND RECOVERY

The heat shock response of L. temulentum cell cultures has been studied at both transcriptional and post-transcriptional levels, using in vitro translation of isolated RNAs, and in vivo labelling of proteins, followed by 1D-PAGE separation. A range of hsps from 100 to 18 kD was observed in vivo. High molecular weight hsps were induced by raising the temperature by as little as 4 degrees C; while low molecular weight hsps required an 8 degrees C temperature rise. Raising the temperature from 25 degrees C to 37 degrees C induced maximum hsp synthesis especially during the second hour of treatment when a 64 kD hsp was observed for the first time. Normal protein synthesis continued at all heat shock temperatures, although the rates oi accumulation of some proteins were temporarily decreased. Under continuous 37 degrees C heat shock, the synthesis of the majority of hsps had ceased by the eighth hour, due largely, but not completely, to an absence of hsp mRNAs. On recovery from heat shock, hsp synthesis continued for the first hour, but had ceased by the fourth hour. Pulse-chase labelling showed that proteins were considerably more unstable at 37 degrees C than at 25 degrees C, but hsps appeared more stable at the higher temperature than control proteins.