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SigK Commitment to sporulation and engulfment (Stages II - III)

SigK during commitment to sporulation

Under the control of both σ^E and SpoIIID, pro-σ^K is synthesized in the mother cell during the engulfment process ¹²³. The sigK gene is composed of two sections made up by two truncated genes called spoIIIC and spoIVCB that are separated from each other by a genetic element called skin (sigmaK intervening) ¹²⁴. During sporulation, and mediated by mother cell-specific recombinase SpoIVCA, site-specific recombination of the DNA at this locus results in the excision of the skin element and rearrangement of the two truncated genes into one coding sigK gene ^{125, 126}. Transcription of this sigK gene gives rise to an inactive precursor (pro-σ^K) that localizes to the membrane ¹²⁷ and requires posttranslational processing before it can execute its activity in transcription of genes that are part of the σ^K regulon ¹²⁸. Crucial checkpoints in the completion of the morphological stage of engulfment as well as intercellular communication ensure avoidance of premature processing, as this event depends on σ^G activity in the forespore. In the absence of these genetic and posttranslational control systems, inappropriate synthesis, activity and accumulation of σ^K result in toxicity and cell lysis ¹²⁹.