Contributions of protein structure and gene position to the compartmentalization of the regulatory proteins σE and SpoIIE in sporulating Bacillus subtilis

Summary At an early stage in endospore formation Bacillus subtilis partitions itself into two dissimilar compartments with unique developmental fates. Transcription appropriate to each compartment is initiated by the activation of compartment-specific RNA polymerase sigma subunits, σE in the mother cell and σF in the forespore. Among the possible factors contributing to the compartment specificity of σE and σF is the selective accumulation of the σE protein in the mother cell and that of SpoIIE, a regulatory phosphatase essential to the activation of σF, in the forespore. In the current work, fluorescent microscopy is used to investigate the contributions of σE and SpoIIE's protein structures, expression and the genetic asymmetry that develops during chromosome translocation into the forespore on their abundance in each compartment. Time of entry of the spoIIE and sigE genes into the forespore was found to have a significant effect on the enrichment of their products in one or the other compartment. In contrast, the structures of the proteins themselves do not appear to promote their transfer to a particular compartment, but nonetheless contribute to compartmentalization by facilitating degradation in the compartment where each protein's activity would be inappropriate.