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  • Title: Analysis of Bacillus subtilis hut operon expression indicates that histidine-dependent induction is mediated primarily by transcriptional antitermination and that amino acid repression is mediated by two mechanisms: regulation of transcription initiation and inhibition of histidine transport.
    Author: Wray LV, Fisher SH.
    Journal: J Bacteriol; 1994 Sep; 176(17):5466-73. PubMed ID: 8071225.
    Abstract:
    Expression of the Bacillus subtilis hut operon is induced by histidine and subject to regulation by carbon catabolite repression and amino acid repression. A set of hut-lacZ transcriptional fusions was constructed and used to identify the cis-acting sites required for histidine induction and amino acid repression. Histidine induction was found to be primarily mediated by transcriptional antitermination at a palindromic sequence located immediately downstream of the first structural gene in the hut operon, hutP. High levels of histidine induction were observed only in hut-lacZ fusions which contained this palindromic sequence. The hutC1 mutation, which results in constitutive expression of the hut operon, was sequenced and found to contain a GC to TA transversion located within the stem-loop structure. Transcription of hut DNA in vitro revealed that the palindromic structure functions as a transcriptional terminator with wild-type hut DNA but not with hutC1 DNA. Two sites were found to be involved in amino acid repression of hut expression: (i) an operator, hutOA, which lies downstream of the hut promoter, and (ii) the hut terminator. The rate of [14C]histidine uptake in amino acid-grown cells was sixfold lower than that seen in cells grown without amino acids. Thus, inhibition of histidine transport in amino acid-grown cells indirectly regulates hut expression by interfering with histidine induction at the hut terminator.
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