Faced with nutritional stress, some bacteria form endospores capable of enduring extreme conditions for long periods of time; yet the function of many proteins expressed during sporulation remains a mystery. We identify one such protein, KapD, as a 3'-exoribonuclease expressed under control of the mother cell-specific transcription factors SigE and SigK in Bacillus subtilis. KapD dynamically assembles over the spore surface through a direct interaction with the major crust protein CotY. KapD catalytic activity is essential for normal adhesiveness of spore surface layers. We identify the sigK mRNA as a key KapD substrate and and show that the stability of this transcript is regulated by CotY-mediated sequestration of KapD. SigK is tightly controlled through excision of a prophage-like element, transcriptional regulation and the removal of an inhibitory pro-sequence. Our findings uncover a fourth, post-transcriptional layer of control of sigK expression that couples late-stage gene expression in the mother cell to spore morphogenesis.
© The Author(s) 2025. Published by Oxford University Press on behalf of Nucleic Acids Research.