The bacteriophage f1 morphogenetic signal and the gene V protein/phage single-stranded DNA complex

The region of the bacteriophage f1 genome near the gene IV/intergenic region (IG) junction previously was shown to contain a sequence necessary for efficient packaging of single-stranded (SS) DNA into phage particles (the f1 "morphogenetic signal") [G. P. Dotto, V. Enea, and N. D. Zinder (1981) Virology 114, 463-473]. The DNA content of f1 phage/pBR322 chimeric plasmid-transformed, phage-infected bacteria has been investigated. The chimeric plasmids, constructed by Dotto et al. (1981), contained the f1 origins of DNA replication and, in some cases, also contained the "morphogenetic signal." Chimeric plasmid SS DNA was detected in phage-infected bacteria harboring any one of these chimeric plasmids, and the majority of this SS DNA was found complexed to the phage gene V protein. Therefore, the "morphogenetic signal" is not required for the formation of the gene V protein/f1 SS DNA complex but instead must function at a later stage of filamentous phage morphogenesis.