Remarkably little is known about the in vivo organization of membrane-associated prokaryotic DNA replication or the proteins involved. We have studied this fundamental process using the Bacillus subtilis phage φ29 as a model system. Previously, we demonstrated that the φ29-encoded dimeric integral membrane protein p16.7 binds to ssDNA and is involved in the organization of membrane-associated φ29 DNA replication. Here we demonstrate that p16.7 forms multimers, both in vitro and in vivo, and interacts with the φ29 terminal protein. In addition, we show that in vitro multimerization is enhanced in the presence of ssDNA and that the C-terminal region of p16.7 is required for multimerization but not for ssDNA binding or interaction with the terminal protein. Moreover, we provide evidence that the ability of p16.7 to form multimers is crucial for its ssDNA-binding mode. These and previous results indicate that p16.7 encompasses four distinct modules. An integrated model of the structural and functional domains of p16.7 in relation to the organization of in vivo φ29 DNA replication is presented.