SITES REQUIRED FOR GLTC-DEPENDENT REGULATION OF BACILLUS-SUBTILIS GLUTAMATE SYNTHASE EXPRESSION

The Bacillus subtilis gltAB genes, coding for the two submits of gluta mate synthase, are transcribed divergently from the gltC gene, encodin g a LysR-type transcriptional activator of gltAB. The predicted gltA a nd gltC transcription start sites are separated by 51 to 52 bp, A 15-b p, consensus binding site (Box I) for LysR-type proteins was found cen tered at position -64 with respect to the gltA transcription start, Th is site was shown by mutational analysis to be required both for GltC- mediated activation of gltA and for autorepression of gltC. Box II, wh ich is similar to Box I, is centered 22 bp downstream of Box I and ove rlaps the -35 region of the gltA promoter, Box II was found to be esse ntial for activation of gltA but not for gltC autoregulation, Introduc tion of approximately one additional helical turn of DNA between Box I and Box II enhanced glt4 expression 7- to 40-fold under nonactivating conditions and about 2-fold under activating conditions. Expression o f gltA was dramatically decreased when the distance between Box I and Box II was altered by a nonintegral number of helical turns of DNA. gl tC autorepression was abolished by most of the inserts between Box I a nd Box II but was augmented by adding one helical turn.