Showing papers on "Nucleolar chromatin published in 2008"

Unreplicated DNA in mitosis precludes condensin binding and chromosome condensation in S. cerevisiae.

Abstract: Condensin is the core activity responsible for chromosome condensation in mitosis. In the yeast S. cerevisiae, condensin binding is enriched at the regions where DNA replication terminates. Therefore, we investigated whether DNA replication completion determines the condensin-binding proficiency of chromatin. In order to fulfill putative mitotic requirements for condensin activity we analyzed chromosome condensation and condensin binding to unreplicated chromosomes in mitosis. For this purpose we used pGAL:CDC6 cdc15-ts cells that are known to enter mitosis without DNA replication if CDC6 transcription is repressed prior to S-phase. Both the condensation of nucleolar chromatin and proper condensin targeting to rDNA sites failed when unreplicated chromosomes were driven in mitosis. We propose that the DNA replication results in structural and/or biochemical changes to replicated chromatin, which are required for two-phase condensin binding and proper chromosome condensation.

The activation of amplified ribosomal RNA genes in the oocytes of Xenopus laevis: an electron microscope analysis.

Abstract: Mitchell, E. L. D. and Hill, R. S. 1987. The activation of amplified rihosomal genes in the oocytes of Xenopus laevis: an electron microscope analysis. —Hereditas 107 219–227. Lund, Sweden. ISSN 0018–0661. Received February 16, 1987 The Miller spreading technique has been used to study the ultrastructure of chromatin from the inactive, amplified ribosomal RNA genes found in the previtellogenic oocytes of Xenopus laevis and to see how this inactive structure is modified during the transcriptional activation of the genes in early vitellogenesis. Inactive, nucleolar chromatin fibres from 300 pm oocytes are packaged into nucleosomal and supranucleosomal structures of 20—-22 nm in diameter. However, where visible, the chromatin axis in active ribosomal genes has a smooth appearance and a diameter of 24 nm. By contrast, the axis of transcription units from lamphrush chromosomes, found in the same preparations, has a distinctively nucleosomal-type of organization. During transcriptional activation, in oocytes of 350–400 pm in diameter, the morphological appearance of the newly-activated genes varies considerably with respect to the length of the gene, the number of RNA polymerase molecules per gene and the amount of RNA transcript associated with the polymerases. However, in oocytes of at least 450 pm, the genes in most, but not all nucleoli, have the classical “Christmas Tree” appearance, consisting of densely packed RNA polymerases and transcripts which show a distinctive gradient in their length from the beginning to the end of the gene.