Summary: The regulatory operon is involved in sucrose induction of the levansucrase gene by an antitermination mechanism. In the presence of sucrose, the activated SacY antiterminator protein stabilizes the secondary structure of a ribonucleic antiterminator sequence (RAT) located in the leader region of the transcript, and overlapping a rho-independent transcription terminator. Formation of the SacY-RAT complex prevents alternative formation of the terminator, allowing transcription of the downstream sequences. In the absence of sucrose, inhibition of SacY activity by SacX leads to termination of transcription. Expression of is also sucrose-inducible. This induction was previously shown to be mediated by SacY itself and/or SacT, another antiterminator involved in induction of genes belonging to a distinct sucrose pathway. These antiterminators are not activated at the same concentration of sucrose. We show here that induction occurs through activation of either SacY or SacT antiterminators, at their respective sucrose activation concentration. This result demonstrates a link between SacY- and SacT-mediated metabolic pathways. In addition, the leader region carries a RAT-like sequence, which however does not appear to overlap any apparent rho-independent transcription terminator. Site-directed mutagenesis experiments on this RAT-like sequence demonstrated its involvement in sucrose induction. Deletions generated in the leader region showed that a palindrome, located 100 nt downstream from the RAT-like sequence, also acts as a -acting element. Computer analysis of the leader RNA suggested that formation of the secondary structure of the RAT-like sequence and the palindrome could be mutually exclusive.


Article metrics loading...

Loading full text...

Full text loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error