BtI is active between about
T2andT6of sporulation and BtII is active from aboutT5on-wards (whereTnis nhours after the end of the exponential
phase). Two sigma factors,s
35
ands
28
, that specifically direct
transcription of cry1Aa from BtI and BtII, respectively were
isolated. In vitro transcription experiments have also indi-cated that othercrygenes (e.g.cry1Ba) contain either BtI alone
or BtI with BtII