MODULATION OF THERMOPROTECTION AND TRANSLATIONAL THERMOTOLERANCE INDUCED BY SEMLIKI FOREST VIRUS CAPSID PROTEIN

Low amounts of Semliki Forest virus capsid protein transferred into ta rget cells by electroporation-mediated delivery (10(3)-10(4) molecules incorporated/cell) confer thermal resistance resulting in enhanced su rvival. Furthermore, when exposed to 43 degrees C, these cells display an enhanced expression of heal-shock protein-70 and a translational t hermotolerance. Similarly, low amounts of capsid protein transferred i nto cells in which transcription is blocked by actinomycin D, also pro tect the translational machinery at 43 degrees C. In a cell-free trans lation system, added capsid protein appears to modulate translational efficiency of endogenous mRNAs. At approximately 1 molecule/ribosome, capsid protein is able to enhance translation at 30 degrees C and at 4 3 degrees C. In contrast, high concentrations of capsid protein are re sponsible for a marked inhibition of protein synthesis at 30 degrees C , but only hamper translational thermotolerance at 43 degrees C. Our r esults favor the hypothesis that small amounts of capsid protein trigg er a chaperone-like activity that is able to protect the translational machinery from thermal damage.