Sequential expression and compartmentalization of sigma factors during sporulation in Bacillus subtilis

Abstract

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.