SpoIIID Commitment to sporulation and engulfment
SpoIIID during commitment to sporulation
The gene encoding SpoIIID is part of the σE regulon and encodes a DNA binding protein that acts both positively and negatively on a subset of σE-regulated genes. It plays an important role in the progression from stage III into stage IV of sporulation by enhancing the expression of genes required for the synthesis of pro-σK 109. Nevertheless, the majority of the σE-dependent genes co-controlled by SpoIIID are repressed by this secondary regulator 95, thereby fine-tuning timing of protein synthesis during sporulation stages II and III in the mother cell. Unique structural structures in its C-terminus allow SpoIIID to bind to both the major and minor groove in the DNA in a monomeric form 112. Through the action of SpoIIID, genes that are involved in the process of engulfment, spore cortex synthesis and the appearance of σK and σG are expressed in pulses that can time-wise be correlated and clustered together according to functionality 95. For instance, short expression pulses of genes encoding some spore outer membrane proteins early in sporulation are necessary to ensure their proper localization before the engulfment process is complete. Also the production of some coat proteins not needed until the final stages of spore coat assembly is delayed by the action of SpoIIID 111, 112.