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Transcription of plasmid DNA in Bacillus pumilus NRS 576.
Formation of endospores by aerobic bacilli serves as a model system for answering basic questions related to development and cyto- differentiation in general. An important aspect of sporulation is that different bacilli seem to form spores by going through the same basic morphological changes. Differentiation begins by the formation of an asymmetric crosswell septum which divides the prespore (forespore) region from the vegetative mother cell. The prespore region becomes engulfed by another layer of membrane to form the double membrane bound forespore. Final maturation occurs with the sequential appearance of cell wall primordium adjacent to the inner forespore membrane, deposition of the mucopeptide cortex within the double membrane, and formation of the proteinaceous coat outside the outer forespore membrane. Concomitant with these morphological changes is an entire battery of biochemical changes which occur during sporulation. Alterations in DNA, RNA, and protein synthesis have been detected in sporulating cells (6). The overall effect is that poor growth conditions derepress regions of the bacterial genome (the precise mechanism is currently not known) which contain the genetic information for making cryptobiotic structures called endospores. Expression of this genetic information results in the disappearance, alteration, or new production of specific proteins, and the production of sporulation specific m-RNA and t-RNA molecules.