Fig. 6. De novo synthesis of a 270 kDa protein in liver tissue of 1-day-old postnatals in response to heat shock (2 h, 42°C). No such response was observed in 18-day-old embryos (score zero in densitometry of both control and heat-shocked individuals). This protein was identified by mass spectrometry analysis as fatty acid synthase (FAS). Each lane represents a different individual. C, control, unexposed individuals; HS, at the end of the heat exposure.