Heat shock induced alterations in polyadenylate metabolism in Drosophila melanogaster

We have studied the effect of heat shock on poly(adenylic acid) [poly(A)] metabolism in Drosophila melanogaster cells by using hybridization of ribonucleic acid (RNA) samples to [3H]poly(uridylic acid). Shortly after heat shock begins, cytoplasmic poly(A) decays rapidly. Two components were detected. Component I constitutes 46% of the total cytoplasmic poly(A) and decays with a half-life of 10 min. Component II (54% of total) is more stable. A half-life was not estimated for component II because new synthesis was not blocked. Studies on the size of cytoplasmic poly(A) indicate component I is completely degraded while component II remains essentially unchanged. Nuclear poly(A) increases rapidly, peaking at 2 or 3 times the normal level after 90 min of heat shock. Studies on the size of nuclear poly(A) indicate the increase is not due to addition of poly(A) to existing poly(A) segments nor appreciably to newly synthesized RNA unless transit time is markedly increased. We conclude that nuclear poly(A) is added in large part to already existing nonadenylated primers. Studies with RNA and protein synthesis inhibitors show RNA and protein synthesis are not required for the changes in poly(A). As the temperature is raised above 34--35 degrees C, the effect on poly(A) metabolism becomes more severe. Changes in external pH, without increased temperature, also alter poly(A) levels. Poly(A) changes may therefore be a rapid response to a variety of physiological factors.