Local protein accumulation during gene activation

Relative values for the dry mass in puff-forming regions of Drosophila hydei salivary gland chromosomes were established with a Leitz double beam interference microscope. All measurements were made after RNA digestion.Optical path differences per unit area of the induced puffs 2-48C and 4-81B (temperature induced) and a cytoplasm-free background were recorded. In each of the nuclei used for these measurements, the same procedure was applied to two reference regions in the vicinity of the puff, region 2, 47A-48B and region 4, 81C-82C respectively. For comparison of the dry mass values of a puff region at various time intervals after the onset of puff induction, ratios of the optical path differences of the puff region over that of the reference region were calculated.These ratios were established at 5, 10, 30, 60 and 120 min after the onset of a temperature treatment and compared with the ratio in non-treated animals. From the data it can be concluded that the dry mass in the induced puffs increases gradually up to 30 min. At this time the dry mass ratio for puff 2-48C has reached a value of 150% and that of puff 4-81B, 210%. It is concluded that this increase in dry mass is due almost entirely to a local accumulation of non-histone protein.