The Puff-like Structure: An Intranuclear Structure for Synthesis of Ribonucleic Acid Polymerase Ⅱ Transcripts as Revealed by the 5-bromouridine-5′-triphosphate Labelling and Immunoelectron Microscopy
Abstract:The puff-like structure (PIS) is an intranuclear structure often observed in cells of higher plants. Several hypotheses regarding the nature of the structure have been put forward while the opinions are still controversial. By using the 5-bromouridine-5‘-triphosphate (BrUTP) labeling technique which was developed in early 90s and has been utilized to localize nascem RNA polymerase Ⅱ (RP Ⅱ ) transcripts, in combination with immunoelectron microscopy. The authors studied PISs in the nuclei of the meristematic cells of Allium cepa L. A large number of gold particles were observed over the PISs of the specimens labelled with BrUTP and anti-BrdU antibody, indicating that RP Ⅱ transcripts were being synthesized actively in the structure. When the specimens were treated with a-amanitin ( 10 μg/L, 2 h) which inhibits the activity of RP Ⅱ, and followed by treatment with BrUTP and anti-BrdU antibody, gold particles in the PLSs of the specimens were decreased dramatically and the gold density of the structure dropped strikingly from 66.65/μm2 to 1.77/μm2, confirming that the gold particles in the structure represented the RP H transcripts. It further demonstrated that the PIS was an intranuclear structure essential for the synthesis of RP Ⅱ transcripts.