22 August 2003
Vol 301, Issue 5636

About The Cover

Cover image expansion

COVER Polytene chromosomes from salivary glands of fruit flies subjected to a brief heat shock (36.5°C for 2.5 min). Heat shock causes parts of the chromatin to decondense, creating puffs, shown here as white regions stained by fluorescent antibodies to a heat shock transcription factor and chromatin transcription and elongation factors. The differential distribution of these factors during heat shock is described on page 1094. [Image: J. Werner and J. T. Lis]