Nucleolar organization as revealed in cycloheximide treated cells.

The nucleolar organisation has been studied in cycloheximide treated rat kangaroo cells. Within 1 h of treatment most nucleoli become loose and reveal a nucleolonemal network. With longer treatment the granules are scarce and the nucleolonemal network becomes more prominent. The network reveals units comparable to the rDNA transcriptional units in length. The nucleolonemal units consists of tufts of fibrils. When cycloheximide is withdrawn, granules reappear and obliterate the nucleolonemal network.