title: Functional and structural heterogeneity of nucleoli: the dependence of the activity of transport of newly synthesized rRNA on nucleolar size and phase of the cell cycle.
abstract: On the basis of radioactivity of interphase cells in the antheridial filaments of Chara vulgaris after a 20 min. incubation with 3H-uridine and after a 40 min. postincubation the activity of synthesis and transport of newly synthesized RNA has been studied in different-sized nucleoli. Investigations of their ultrastructure have been also performed. It was found that the smallest nucleoli from 0.2-0.5 micron in diameter indicate the structure typical of nucleoli inactive in RNA synthesis. Nucleoli ranging from 0.5-2.0 microns in diameter which constitute the most numerous population were evidenced to be active both in synthesis and transport of newly synthesized RNA. Their structure is characterized by nucleoloneme-like appearance with small quantity of granular components. The largest nucleoli which are present in small numbers at the onset of interphase gradually increase in number till G2 phase. They indicate similar transcriptional activity as the latter category of nucleoli but a lower activity of transport of newly synthesized RNA; moreover, they abound in granular components surrounding the nucleoloneme. Nucleoli from all size-classes increase their transcriptional activity in middle S and middle G2 phases. Transport of newly synthesized RNA, however, is differentiated and it depends on both the phase of the cell cycle and nucleolar size.
mesh_terms: D002453:Cell Cycle; D002466:Cell Nucleolus / Q000378:metabolism* / Q000648:ultrastructure; D056890:Eukaryota / Q000166:cytology / Q000378:metabolism; D008854:Microscopy, Electron; D012323:RNA Processing, Post-Transcriptional; D012335:RNA, Ribosomal / Q000378:metabolism*; D013997:Time Factors; D014529:Uridine / Q000378:metabolism
chemical_list: D012335:RNA, Ribosomal; D014529:Uridine