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 studie d at both transcriptional and post-transcriptional levels, using in vi tro translation of isolated RNAs, and in vivo labelling of proteins, f ollowed by 1D-PAGE separation. A range of hsps from 100 to 18 kD was o bserved in vivo. High molecular weight hsps were induced by raising th e 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 espec ially during the second hour of treatment when a 64 kD hsp was observe d for the first time. Normal protein synthesis continued at all heat s hock 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 recove ry from heat shock, hsp synthesis continued for the first hour, but ha d ceased by the fourth hour. Pulse-chase labelling showed that protein s 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.