1887

Abstract

Differential expression of the 57.I urease operon in response to pH is effected by repression of transcription from a proximal promoter, . To localize the -acting elements involved in the regulation of the urease operon, the intact promoter region and its derivatives were generated and fused to a promoterless chloramphenicol acetyltransferase () gene. The promoter– fusions were established in the gene of by using a newly constructed integration vector. CAT-specific activities were examined in batch-grown cells at pH 75 and 55. The results indicated that a 21 bp region immediately 5′ to the −35 element was required for efficient repression of at neutral pH and that the 39 bp (−57 to −95) 5′ to this region contained sequences required for optimal expression of . A potential secondary repressor-binding site was tentatively identified further upstream of the −35 element (−96 to −115). To further analyse the -acting elements, base changes were introduced into two AT-rich repeats within the primary repressor-binding site. One such derivative, M1, with five base substitutions immediately 5′ to the −35 element, expressed 20-fold more CAT-specific activity at neutral pH than the strain carrying wild-type . Also, the pH sensitivity of strain M1 was greatly reduced, suggesting that this AT-rich region is crucial for repression of the urease operon. Deletion of three consecutive 15- or 16-base segments from −52 to −96 in the M1 background resulted in lower activities compared to strain M1, confirming the presence of sequences required for optimal expression of the operon. All of the fusions were also integrated into the gene of DL1, a non-ureolytic oral sp. Repression of was observed at neutral pH in and the effects of the various mutations of the repressor-binding site largely paralleled those seen in , suggesting that the -elements may be a target for a global regulatory circuit that controls gene expression in streptococci in response to pH.

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2002-11-01
2020-06-05
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