title: Electron microscope tomography: transcription in three dimensions.
abstract: Three-dimensional reconstruction of an asymmetric biological ultrastructure has been achieved by tomographic analysis of electron micrographs of sections tilted on a goniometer specimen stage. Aligned micrographs could be displayed as red-green three-dimensional movies. The techniques have been applied to portions of in situ transcription units of a Balbiani ring in the polytene chromosomes of the midge Chironomus tentans. Current data suggest a DNA compaction of about 8 to 1 in a transcription unit. Nascent ribonucleoprotein granules display an imperfect sixfold helical arrangement around the chromatin axis.
mesh_terms: D000818:Animals; D002683:Chironomidae / Q000235:genetics / Q000648:ultrastructure; D002843:Chromatin / Q000648:ultrastructure; D004247:DNA / Q000378:metabolism; D008854:Microscopy, Electron / Q000379:methods*; D012261:Ribonucleoproteins / Q000378:metabolism; D014054:Tomography / Q000379:methods*; D014158:Transcription, Genetic
chemical_list: D002843:Chromatin; D012261:Ribonucleoproteins; D004247:DNA