the sarr mutant as compared to the parental strain taken together these data demonstrate that sarr is a dna binding protein that binds to the sara promoter to down regulate sara expression the level of sara has been shown to correlate with the extent of agr activation 20 northern analysis of sarr mutant alc1713 with an agra rnaii probe confirmed a higher level of rnaii expression as compared with the parental control fig8 b collectively these data demonstrate that sarr down regulates sara expression by binding to the sara promoter to down modulate sara p1 transcription the end result is the modulation of target genes e g agr downstream of the sara regulatory cascade the intact 345 bp sarr gene was amplified by pcr using chromosomal dna from s aureus strain rn6390 as the template and primers containing flanking restriction sites ndei and bamhi to facilitate cloning into an expression vector pmal c2 biolabs beverly mass modified by truncating 21 residues from the linker region that connects sarr and mbp the recombinant plasmid containing the sarr gene was transformed to e coli bl21 de3 plyss enhanced expression of sarr mbp fusion was induced by adding iptg isopropyl 1 thio b d galactopyranoside to a 4.