VapX and VapD heterodimerize in vivo. 86-028NP vapX or vapD was fused to the LexA DNA binding domain (DBD) in the vectors pSR658 or pSR659, resulting in pDD882 or pDD884, respectively. Reciprocally, vapD or vapX was also fused to the LexA DBD in the vectors pSR658 or pSR659, resulting in pDD885 or pDD883, respectively. Each pair was co-transformed into the reporter strain SU202 and the amount of heterodimerization was quantitated by β-galactosidase activity assays (n = 3 in triplicate). Data are expressed as mean ± SD.