Regulation of haemolysin synthesis in E. coli determined by HLY genes of human origin.

We have previously reported the secretion of a 107K polypeptide into the medium from a haemolytic E. coli K12 strain (Mackman and Holland 1984a). In addition, we demonstrated that haemolysin production was correlated with the presence of this polypeptide in the growth medium in a large number of E. coli isolates of human and animal origin (Mackman and Holland 1984b). In this paper we confirm that the 107K polypeptide is indeed haemolysin: both haemolytic activity and the 107K polypeptide show a similar pattern of accumulation during the growth cycle; identical levels are produced in three different growth media; they have the same half-life in minimal medium. The results also show that the expression of haemolysin is not influenced by the growth medium or subject to catabolite repression. However, expression is apparently switched off as cells enter the late exponential phase of growth. Finally, we present data indicating that the previously reported variation in haemolysin production in different media is entirely due to the instability of the haemolysin itself. Degradation of the 107K polypeptide in the medium was accompanied by the accumulation of a major breakdown product of 60K.