ATP-DEPENDENT NUCLEOSOME RECONFIGURATION AND TRANSCRIPTIONAL ACTIVATION FROM PREASSEMBLED CHROMATIN TEMPLATES

GAL4-VP16-mediated nucleosome reconfiguration and transcriptional acti vation were observed with preassembled chromatin templates that contai ned regular and physiological nucleosome spacing. Both processes were dependent on adenosine triphosphate (ATP), although binding of GAL4-VP 16 to the chromatin was ATP-independent. Factor-mediated nucleosome re configuration was not, however, sufficient for transcriptional activat ion. These experiments recreate in vitro the active participation of n ucleosomal cores in the regulation of transcription that occurs in viv o, and they suggest a multistep pathway for transcriptional activation in which factor- and ATP-dependent nucleosome reconfiguration is foll owed by facilitation by the DNA-bound activator of transcription from the repressed chromatin template.