Minus-strand origin of filamentous phage versus transcriptional promoters in recognition of RNA polymerase

Replication of complementary-strand DNA in filamentous phages is initiated by a primer RNA that is synthesized at the minus-strand origin on the viral single-stranded DNA by Escherichia coli RNA polymerase holoenzyme containing the σ⁷⁰ subunit. We have demonstrated that the affinity of RNA polymerase in vitro to the origin is about 16-fold higher than that to the lacUV5 promoter. We have also shown that the temperature dependence of the primer RNA synthesis is much lower than that of lacUV5 transcription. The high affinity of RNA polymerase to the origin depends on the single strandedness of the '-10 region.' A nucleotide sequence of the nontemplate strand in the -10 region was found to be important for the function, but that of the template strand was not. These observations suggest that σ⁷⁰ subunit directly interacts with the single-stranded nontemplate strand containing adenine residue(s) at the -10 region of promoter.