SpoVID guides SafA to the spore coat in Bacillus subtilis

Bacteria assemble complex structures by targeting proteins to specific subc ellular locations. The protein coat that encases Bacillus subtilis spores i s an example of a structure that requires coordinated targeting and assembl y of more than 24 polypeptides. The earliest stages of coat assembly requir e the action of three morphogenetic proteins: SpoIVA, CotE, and SpoVID, In the first steps, a basement layer of SpoIVA forms around the surface of the forespore, guiding the subsequent positioning of a ring of CotE protein ab out 75 nm from the forespore surface. SpoVID localizes near the forespore m embrane where it functions to maintain the integrity of the CotE ring and t o anchor the nascent coat to the underlying spore structures. However, it i s not known which spore coat proteins interact directly with SpoVID, In thi s study we examined the interaction between SpoVID and another spore coat p rotein, SafA in vivo using the yeast two-hybrid system and in vitro. We fou nd evidence that SpoVID and SafA directly interact and that SafA interacts with itself, Immunofluorescence microscopy showed that SafA localized aroun d the forespore early during coat assembly and that this localization of Sa fA was dependent on SpoVID. Moreover, targeting of SafA to the forespore wa s also dependent on SpoIVA, as was targeting of SpoVID to the forespore, We suggest that the localization of SafA to the spore coat requires direct in teraction with SpoVID.