The N-terminal and C-terminal domains of RAP1 are dispensable for chromatin opening and GCN4-mediated HIS4 activation in budding yeast

Repressor activator protein 1 (RAP1) assists GCN4-mediated HIS4 activation by overcoming some repressive aspect of chromatin structure to facilitate G CN4 binding. RAP1 also participates in other nuclear processes, and discret e domains of RAP1 have been shown to have specific properties including DNA binding, DNA bending, transcriptional activation, and silencing and telome re functions. To investigate whether specific domains of RAP1 are required to "open" chromatin and help GCN4 to activate the HIS4 gene, we examined th e abilities of different truncated RAP1 proteins to perturb positioned nucl eosomes via a nucleosomal RAP1 site in a yeast episome in vivo, and we test ed HIS4 activation in yeast strains harboring truncated RAP1 mutants. We fo und that neither the DNA bending domain nor the putative activation domain of RAP1 is required for its ability to perturb the chromatin structure of a plasmid containing a RAP1 site. Similarly, neither the putative activation domain nor the N-terminal DNA-bending domain was required for GCN4-mediate d activation of HIS4. We also used a rap1(ts) mutant to show that continuou s occupancy of the HIS4 promoter by RAP1. is required for GCN4-mediated gen e activation.