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.