The enhancers and promoters of the Xenopus laevis; ribosomal spacer are associated with histones upon active transcription of the ribosomal genes

摘要

The presence of histones on the enhancer-promoter region of the X.laevis ribosomal spacer has been studied in embryos at stage 40, where the ribosomal genes are actively transcribed. Isolated tadpole nuclei were either fixed with formaldehyde or irradiated with UV laser to crosslink histones to DNA. The purified protein-DNA complexes were immunoprecipltated with antibodies to the histones H1, H2A and H4 and the DNA fragments carrying the respective histones were analyzed for the presence of spacer enhancer-promoter sequences by hybridization to specific DNA probe. The two independent crosslinking procedures revealed the presence of these DNA sequences in the precipitated DNA. The quantitative analysis of the UV laser-crosslInked complexes showed that histones H2A and H4 were associated with enhancer-promoter DNA in amounts similar to those found for bulk DNA, whilst the content of H1 was reduced.