ARCHITECTURAL SPECIFICITY IN CHROMATIN STRUCTURE AT THE TATA BOX IN-VIVO - NUCLEOSOME DISPLACEMENT UPON BETA-PHASEOLIN GENE ACTIVATION

Extensive studies of the beta-phaseolin (phas) gene in transgenic toba cco have shown that it is highly active during seed embryogenesis but is completely silent in leaf and other vegetative tissues, In vivo foo tprinting revealed that the lack of even basal transcriptional activit y in vegetative tissues is associated with the presence of a nucleosom e that is rotationally positioned with base pair precision over three phased TATA boxes present in the phas promoter. Positioning is sequenc e-dependent because an identical rotational setting is obtained upon n ucleosome reconstitution in vitro, A comparison of DNase I and dimethy l sulfate footprints in vivo and in vitro strongly suggests that this repressive chromatin architecture is remodeled concomitant with gene a ctivation in the developing seed. This leads to the disruption of hist onemediated DNA wrapping and the assembly of the TATA boxes into a tra nscriptionally competent nucleoprotein complex.