sentences:  Four molecules of Fis bind to this site as a homodimers and are required for the recombination reaction to proceed.The initial reaction requires binding of Hin and Fis to their respective DNA sequences and assemble into a higher-order nucleoprotein complex with branched plectonemic supercoils with the aid of the DNA bending protein HU.At this point, it is believed that the Fis protein modulates subtle contacts to activate the reaction, possibly through direct interactions with the Hin protein.