Sporulation of
Bacillus subtilis is induced by the deprivation of the nutrients in the medium. During sporulation more than 50 sporulation qenes (
spo) are expressed sequentially. The sequential expression of
spo genes is regulated mainly at the level of transcription, which is governed by the cascades of five sporulation-specific sigma factors, σ
H, σ
F, σ
E, σ
G, and σ
K, At the initiation of sporulation, the first sporulation specific sigma factor σH is activated, which then activates
spoIIA operon encoding the second sigma factor σ
F. Expression of
spoIIA and
spoIIE operons is required for the activation of the pro-σ
E, the inactive precursor of the third sigma factor σ
E, which is required for the expression of the fourth sigma factor σ
G. σ
G is present only in the forespore, but its function is required for the activation of the pro-σ
K, which is present only in the mother cell. sigK gene encoding σ
K is construted by the mother cell-specific DNA rearrangement occurring during the middle stage of sporuation.
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