ORGANIZATION OF TRANSCRIBED AND NON-TRANSCRIBED CHROMATIN IN ISOLATED-NUCLEI OF ZEA-MAYS ROOT-CELLS

  • 1 January 1981
    • journal article
    • research article
    • Vol. 23  (2) , 303-311
Abstract
A slightly modified technique of Miller was applied to nuclei isolated from roots of germinating corn embryos. Under the conditions used, the extranucleolar chromatin was easily spread but the nucleolar chromatin often remained aggregated. The nontranscribed chromatin regions consisted of long deoxyribonucleoprotein (DNP) fibrils with the typical beads-on-a-string appearance of nucleosomal arrangement. When the EDTA concentration of the spreading medium was increased, linear arrangement of nucleosomes, 20 nm and 40-50 nm DNP granules were also closely packed without any apparent order. Independently of the EDTA concentration, numerous nonnucleolar ribonucleoprotein (RNP) fibrils with a knobby structure were seen laterally bound to DNP fibrils. These knobby RNP fibrils (transcripts) were highly folded and appeared in bunch-of-grapes configurations. Each RNP knob measured 23 nm in diameter and the longest of these RNP fibrils were estimated to reach 1.5 .mu.m. The RNP fibrils were often solitary and never exceeded 8/10 .mu.m of the DNP axis. Distribution, morphology and size of these transcripts distinguished them from the nucleolar Christmas-tree-like figures. These nonnucleolar transcriptional units may correspond to genes coding for the heterodisperse nuclear RNA (hnRNA) and the knobs of 23 nm could be related to informofers or hnRNA particles.