The Bacillus SpoIIGA protein is targeted to sites of spore septum formation in a SpoIIE-independent manner.
The process of bacterial cell division involves the assembly of a complex of proteins at the site of septation that probably provides both the structural and the cytokinetic functions required for elaboration and closure of the septal annulus. During sporulation in Bacillus subtilis, this complex of proteins is modified by the inclusion of a sporulation-specific protein, SpoIIE, which plays a direct role in gene regulation and also has a genetically separable role in determining the gross structural properties of the specialized sporulation septum. We demonstrate by both green fluorescent protein (GFP) fusions and indirect immunofluorescence microscopy that SpoIIGA, a protein required for proteolytic cleavage of pro-sigmaE, is also targeted to the sporulation septum. Septal localization of SpoIIGA-GFP occurred even in the structurally abnormal septum formed by a SpoIIE null mutant. We also report the isolation of a spoIIGA homologue from Bacillus megaterium, a species in which the cells are significantly larger than those of B. subtilis. We have exploited the physical dimensions of the B. megaterium sporangium, in conjunction with wide-field deconvolution microscopy, to construct three-dimensional projections of sporulating cells. These projections indicate that SpoIIGA-GFP is initially localized in an annulus at the septal periphery and is only later localized uniformly throughout the septa. Localization was also detected in a B. subtilis spo0H null strain that fails to construct a spore septum. We propose that SpoIIGA is sequestered in the septum by an interaction with components of the septation machinery and that this interaction begins before the construction of the asymmetric septum.
Fawcett
P
P
University of Georgia, Department of Genetics, Athens 30602, USA.
Melnikov
A
A
Youngman
P
P
D000595:Amino Acid Sequence; D001410:Bacillus megaterium / Q000378:metabolism*; D001412:Bacillus subtilis / Q000235:genetics / Q000378:metabolism*; D001413:Bacillus thuringiensis / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003013:Clostridium / Q000235:genetics; D017124:Conserved Sequence; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010447:Peptide Hydrolases; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012808:Sigma Factor; D013171:Spores, Bacterial; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D001426:Bacterial Proteins; D008164:Luminescent Proteins; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D012808:Sigma Factor; C087737:Spo0H protein, Bacillus subtilis; D014157:Transcription Factors; C092468:spoIIR protein, Bacillus subtilis; C030069:spore-specific proteins, Bacillus; D049452:Green Fluorescent Proteins; D010447:Peptide Hydrolases; C071976:SpoIIGA protein, Bacillus subtilis