Selective expression of a plasmid cat gene at a late stage of Bacillus subtilis sporulation.

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Abstract
The cat-86 gene in plasmid pPL603 specifies chloramphenicol acetyltransferase (CAT) and is selectively expressed in B. subtilis at a stage in sporulation in which internal spores are first observed (approximately T8). The gene is unexpressed in vegetatively growing cells. cat-86 expression and spore formation are blocked when cells are grown in excess glucose. cat-86 expression at T8 is due to selective transcription of the gene, since cat-86 mRNA is undetectable in vegetatively growing cells but is readily demonstrated in sporulating cells. The transcription start site for cat-86 mRNA from sporulating cells is within a 203-base-pair restriction fragment designated P1, which is located upstream from the cat coding region on pPL603. Deletion of P1 from pPL603 eliminates the sporulation-associated expression of cat-86. Host sporulation genes, whose function is absolutely required for cat-86 expression at T8, include 6 early sporulation (spo0) genes and spoIIe. pPL603 provides a novel system in which the in vivo expression of a known, plasmid-linked gene is dependent on sporulation-specific changes in B. subtilis.