Fig 7. Mutation of the Walker A motif of SpoIIIAA leads to defects in spore formation.

TEM analyses of wildtype carrying empty vector (WT/EV) and spoIIIA ⁻(IIIA ^–) strains carrying empty vector (EV), or spoIIIA complementation constructs encoding the wildtype operon (IIIA), a K167A Walker A mutation (K167A), D244A Walker B mutation (D244A), and K167A/D244A double mutation (K167A/D244A). The forespore region of these strains is shown on the right. Black arrows indicate regions that resemble coat layers surrounding the forespore. White arrows indicate coat that appears anchored to the leading edge of the engulfing membrane but is not intimately associated with the mother cell-forespore interface. Scale bars represent 500 nm. The efficiency of heat-resistant (HR) spore formation was determined for each strain relative to WT for at least three biological replicates. Engulfment complete (EC) cells designates the number of cells in the population that completed engulfment out of at least 50 sporulating cells that had initiated engulfment or progressed beyond this stage.