Puffing and histone acetylation in polytene chromosomes.

Fixation with picric acid or formaldehyde retains incorporated [(3)H]acetate which is lost after fixation with ethanol and acetic acid. Unlike [(3)H]uridine, [(3)H]acetate is diffusely incorporated into polytene chromosomes, and not preferentially into existing or newly induced puffs. It is suggested that puff formation does not include an acetylation of histones.