INTERACTIONS OF WILD-TYPE AND TRUNCATED LEVR OF BACILLUS-SUBTILIS WITH THE UPSTREAM ACTIVATING SEQUENCE OF THE LEVANASE OPERON

Transcription of the levanase operon of Bacillus subtilis is controlle d by LevR, an activator of the NifA/NtrC family of regulators. An upst ream activating sequence (UAS) located in a 16 bp palindromic structur e has previously been characterized. LevR was overproduced in B. subti lis and interaction between the activator and the UAS was demonstrated by gel shift and footprint experiments. The LevR protein specifically binds to the two-halves of the palindromic structure centered at -125 bases upstream from the transcriptional start site. In addition, foot print analysis suggests that LevR interacts with a third DNA region lo cated at positions -90 to -80. To investigate the function of the diff erent domains of the LevR activator, stop codons were introduced at va rious positions in the levR gene. The ability of the truncated LevR po lypeptides to activate transcription, to respond to the inducer or to interact with the UAS was tested. The results obtained suggest that Le vR is a multidomain protein. The amino-terminal part of the protein is required for DNA binding whereas the central domain allows the activa tion of transcription. The carboxy-terminal region is involved in the modulation of the LevR activity by the inducer.