A region of the filamentous phage phi Lf genome that can support autonomous replication and miniphage production.

A 2028-bp fragment from the RF DNA of phi Lf, a filamentous phage of Xanthomonas campestris pv. campestris, was maintained autonomously as a minireplicon. Upon superinfection of the cells harboring the minireplicon with phi Lf, transducing miniphage particles were released. The minireplicon contained an open reading frame (ORF346) able to encode a polypeptide of MW39144, which possessed consensus motifs found in the Rep proteins from various sources. These findings suggested ORF346 to be the gene encoding replication initiation protein, gene II (gII) of phi Lf. Upstream to ORF346 were sequences with potential to form hairpin structures and a sequence similar to the integration host factor (IHF) binding site, structures similar to the intergenic region (IR) of the Ff phages. A 15 bp AT-rich core for phi Lf integration was found 37 bp downstream to the IHF binding site.