ANALYSIS OF TRIMETHYLPSORALEN PHOTOREACTIVITY TO Z-DNA PROVIDES A GENERAL INVIVO ASSAY FOR Z-DNA - ANALYSIS OF THE HYPERSENSITIVITY OF (GT)N B-Z JUNCTIONS

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  • 1 June 1988
    • journal article
    • research article
    • Vol. 6  (6) , 532-+
Abstract
We have described an exonuclease III/photoreversal procedure to map, with base pair resolution, the bases which have photoreacted with 4,5'',8-trimethylpsoralen (Me3-psoralen) forming forming either monoadducts or interstrand cross-links in DNA (20). This assay allows quantitation of relative rates of Me3-psoralen photobinding to bases in DNA at levels as low as one cross-link per 8,000 base pairs. This assay should be useful for a wide variety of applications of Me3-psoralen photobinding to DNA. Here, we demonstrate the applicability of the Me3-psoralen exo III assay for analysis of the conformation of the Z forming sequences (GT)12ATGT and GAATTC(TG)6TA(TG)6. We have shown previously that Me3-psoralen forms crosslinks in the 5''TA within the (CG)6TA(CG)6 sequence when it exists in the B conformation but not when it exists in the Z conformation (34). More recently we have confirmed this result with the exo III assay and have shown at least a hundred fold increase in Me3-psoralen photoreactivity at the 5''AT sequence within the EcoR I sites (GAATTC) which presumably represent B-Z junctions flanking (CG)6TA(CG)6 (20). Here we demonstrate both the characteristic decrease in psoralen photobinding to 5''TAs within (GT)12ATGT and (TG)6-TA(TG)6 and the hyperreactivity of B-Z junctions. These characteristic properties of Me3-psoralen photobinding provide an assay for Z-DNA that is applicable in vivo. The general applicability of this approach for assaying Z-DNA in vivo is discussed.

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