Varied Transcriptional Efficiencies of Multiple ArabidopsisU6 Small Nuclear RNA Genes Transcriptive Sites of RNA PolymeraseⅠin the Nucleolus of Triticum aestivum Revealed by BrUTP Labelling and Immunoelectron Microscopy 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 Cloning and Sequencing of rpoA Gene from Rice Chloroplast Genume