Yeast two-hybrid system was modified to allow easy detection of prokaryotic protein-protein interactions. Three plasmids (pGBR1, pGBR2, pGBR3) with the ClaI restriction site shifted in the three possible reading frames in fusion with GAL4 activating domain were constructed. The modified plasmids were used for identification of protein partners of FtsZ from Bacillus subtilis. Among partners of FtsZ the FtsA protein and a globular part of the SpoIIE protein were identified. The protein interactions were quantified by measurements of beta-galactosidase activity in yeast cells using 4-methylumbelliferyl beta-D-galactopyranoside as fluorogenic substrate.