a symmetrical mode of replication has been suggested, whereby protein-primed initiation occurs non-simultaneously from either end of the chromosome; this involves two replication origins and two distinct polymerase monomers. synthesis is continual and involves a strand displacement mechanism. this was demonstrated by the ability of the enzyme to continue to copy the singly primed circular genome of the m13 phage more than tenfold in a single strand (over 70kb in a single strand).