ISSN:
1617-4623
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary As a first approach towards studying the regulation of hemolysin synthesis in Escherichia coli, we have fused lacZ into the four hly genes (hlyC, hlyA, hlyB a and hlyB b) using the Mud-1 (Mu::lacZ, Y, Apr) phage. The sites of insertion of Mud-1 within the various hly genes of the Hly plasmid pHly152 were determined by the hemolytic phenotype of the Hly- mutants (Hly ex - /Hly in - or Hly ex - /Hly in + ) and by complementation of these Hly- mutants with recombinant plasmids carrying cloned hly genes. It was found that hlyC, hlyA and hlyB a are transcribed from a relatively weak promoter (hlypL) located in front of hlyC. The activity of β-galactosidase is considerably lower when Mud-1 is integrated in hlyB a than when it is inserted in hlyC, suggesting a considerable decline in hly gene expression from hlyC to hlyB a. The DNA sequence upstream of the coding region of hlyC was found to promote galK gene expression when a fragment covering this region was inserted into the promoter-probe vector pKO-11. A putative promoter sequence, which could correspond to hlypL, was identified in this sequence. The hlyB b gene appears to be transcribed from a different promoter and the direction of transcription seems to be opposite to that of the hlyC, A, B a operon. The strength of this promoter (hlypR), based on the level of β-galactosidase activity of Mud-1 insertion mutants in hlyB b, is considerably higher than that of hlypL. The hly::lacZ fusions were also used to study a possible regulatory control of the hly genes on the transcriptional level by various physiological conditions (cAMP, media composition, growth phase), which have been shown to affect the synthesis of hemolysin. It was found that none of these conditions influence the expression of β-galactosidase, ruling out the possibility that transcription of the hly genes is modulated by these conditions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00330963
