Easily-controllable, helper phage-free single-stranded phagemid production system

Single-stranded (ss) DNAs are utilized in various molecular biological and biotechnological applications including the construction of double-stranded DNAs with a DNA lesion, and are commonly prepared by using chimeric phage-plasmids (phagemids) plus M13-derived helper phages. However, the yields of ss DNA with these methods are poorly reproducible, and multiple factors must be optimized.

In this report, we describe a new arabinose-inducible ss phagemid production method without helper phage infection. The newly exploited DNA derived from VCSM13 expresses the pII protein, which initiates ss DNA synthesis, under the control of the araBAD promoter. In addition, the packaging signal is deleted in the DNA to reduce the contamination of the phage-derived ss DNA. The phagemid DNA of interest, carrying the M13 origin of replication and the packaging signal, was introduced into bacterial cells maintaining the modified VCSM13 DNA as a plasmid, and the ss phagemid DNA production was induced by arabinose. The DNA recovered from the phage particles had less contamination from VCSM13 DNA, as compared to the conventional method. Moreover, we extended the method to purify the ss DNAs by using an anion-exchange column, to avoid the use of hazardous chemicals.

Using this combination of methods, large quantities of phagemid ss DNAs of interest can be consistently obtained.