Structural transitions of chromatin in isolated XXXX erythrocyte nuclei. I. The effects of ions.

@entity1238 @entity3281 @entity13718 @entity8723 @entity1897 @entity3282 @entity4338 @entity526
Nuclei from @entity1238 erythrocytes have been isolated under varying ionic conditions and their morphology studied by light and electron microscopy. The 200-A beaded chromatin fibre observed in vivo is maintained in media containing @entity8723 or @entity3282 , but not in those containing @entity3281 as the sole divalent cation. In the absence of these alkaline-earth metal ions, 100-A filaments predominate. This suggests that the native 200-A fibre in isolated nuclei is also stabilized by specific divalent cations. Gross chromatin condensation within the nucleus occurs independently of whether the chromatin is in the form of 100-A or 200-A fibres, but requires the presence of divalent cations. Lower concentrations of @entity8723 or @entity3282 are necessary as compared with @entity13718 . In the presence of sufficient divalent cations, decreasing @entity4338 concentration causes @entity1897 , the condensation of chromatin towards the nuclear membrane. Monovalent cation alone does not appear capable of inducing @entity1897 . The transcriptional capacities of the different morphological types identified have been studied using @entity526 RNA polymerase as a probe. Neither the degree of chromatin condensation nor the state of higher-order coiling have a significant effect on the rate of transcription of the DNA. These results are discussed with regard to further in vitro studies on eukaryotic gene activity.
