SUBUNIT COMPOSITION AND DOMAIN-STRUCTURE OF THE SPO0A SPORULATION TRANSCRIPTION FACTOR OF BACILLUS-SUBTILIS

The Spo0A transcription factor is responsible for the initiation of sp orulation and is active in transcription only after phosphorylation by a specific signal transduction pathway, the phosphorelay. The effect of phosphorylation on the physical properties of Spo0A was determined. Spo0A and Spo0A similar to P both behaved as monomers during Sephacry l chromatography and gel electrophoresis, suggesting that phosphorylat ion did not modify the oligomerization state of the protein. Trypsin d igested Spo0A at a single cleavage site between residues 142 and 143 w ithin a hinge connecting two tightly folded domains. The amino domain retains ability to be phosphorylated by the phosphorelay. The carboxyl domain is active as a DNA-binding protein and retains the sequence sp ecificity of the intact molecule for 0A boxes on the abrB promoter as revealed by footprinting studies. The carboxyl domain stimulated in vi tro transcription from the spoIIG promoter 5-fold greater than an equa l amount of Spo0A and about half as well as equivalent amounts of Spo0 A similar to P. Thus, the unphosphorylated amino domain inhibits the t ranscription stimulation activity of the carboxyl domain. We suggest t hat phosphorylation activates transcription regulation functions of Sp o0A by modifying the spatial relationships of the amino and carboxyl d omains.