Efficient and Reliable Production of Vectors for the Study of the Repair, Mutagenesis, and Phenotypic Consequences of Defined DNA Damage Lesions in Mammalian Cells

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

Background

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.

Results

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.

Conclusion

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

Transcriptional mutagenesis reduces splicing fidelity in mammalian cells

Splicing fidelity is essential to the maintenance of cellular functions and viability, and mutations or natural variations in pre-mRNA sequences and consequent alteration of splicing have been implicated in the etiology and progression of numerous diseases. The extent to which transcriptional errors or lesion-induced transcriptional mutagenesis (TM) influences splicing fidelity is not currently known. To investigate this, we employed site-specific DNA lesions on the transcribed strand of a minigene splicing reporter in normal mammalian cells. These were the common mutagenic lesions O⁶-methylguanine (O⁶-meG) and 8-oxoguanine (8-oxoG). The minigene splicing reporters were derived from lamin A (LMNA) and proteolipid protein 1 (PLP1), both with known links to human diseases that result from deregulated splicing. In cells with active DNA repair, 1–4% misincorporation occurred opposite the lesions, which increased to 20–40% when repair was compromised. Furthermore, our results reveal that TM at a splice site significantly reduces in vivo splicing fidelity, thereby changing the relative expression of alternative splicing forms in mammalian cells. These findings suggest that splicing defects caused by transcriptional errors can potentially lead to phenotypic cellular changes and increased susceptibility to the development of disease.