6533b861fe1ef96bd12c5a0c

RESEARCH PRODUCT

Different micrococcal nuclease cleavage patterns characterize transcriptionally active and inactive sea-urchin histone genes.

subject

description

Micrococcal nuclease (MNase) and DNaseI have made a great contribution to our present understanding of the structural organization of the eucaryotic genome [l - 31. The enhanced sensitivity of active portions of the genome to DNaseI gave, in fact, the first indication of differences in the nucleoproteic arrangement of the transcribed as compared to the silent DNA regions [4]. The use of MNase, as a probe of the chromatin organization of specific genes in the active and inactive state, provided additional evidence for this and further showed that the packing of several coding segments of DNA in a regular array of nucleosomal particles is severely but reversibly affected by the transcriptional process per se [5 - 71. The discovery of several sites hypersensitive to DNaseI, and in some instances at least also to MNase, in the neighbourhood of (potentially) active genes [8 - 111 has recently proved very useful for the identification of the DNA regions which, often through sequence-specific interactions with proteic factors, modulate gene expression [12- 161. As an approach to the study of the control elements involved in the transcriptional regulation of the sea-urchin genome during development, we have undertaken an analysis of the structural arrangement of the set of histone genes actively transcribed during the early stages of embryogenesis [17 - 191. As previously reported, the nucleosomal arrangement of these genes is dramatically perturbed and the overall nuclease sensitivity is enhanced when they are transcribed, to become indistinguishable from that of bulk chromatin at later stages of development [7, and unpublished results].