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Publisher Summary The early studies led to investigations into the physiological and genetic basis for enterotoxin production by sporulating C. perfringens cells. Using DS medium, Duncan constructed a fairly precise kinetic analysis of sporulation, enterotoxin synthesis, and release of the mature spore by the mother cell during the growth and sporulation cycle of C. perfringens type A strain NCTC 8798. Genetic evidence in support of the coregulation of sporulation and Clostridium perfringens enterotoxin (CPE) synthesis was provided by the analysis of spontaneous and chemical sporulation mutants of CPE+ C. perfringens type A strain NCTC 8798. During the sporulation cycle, CPE synthesis appears to be regulated at the transcriptional level. The levels of both cpe mRNA and protein rose rapidly in synchrony, about 1 hour after the cells entered stationary phase, indicating that the increase in CPE expression as cells enter sporulation results from increased transcription of the cpe gene. Expression of CPE in Escherichia coli is useful as a heterologous host system for identifying gene products that regulate cpe expression. CPE expression is detected by the E. coli transformants, even though naturally nonenterotoxigenic C. perfringens transformants carrying the same shuttle plasmid are able to produce significant levels of CPE.