The interaction of 4′-N(2-aminoethyl)aminomethyl-4, 5′,8- trimethylpsoralen-modif led 01 igonucleoside methyiphosphonates with synthetic ds-DNA containing a T7 RNA polymerase promoter was studied. The oligomers effectively crosslin.ked with either coding or noncoding as-DNA when irradiated at 365 rim, but not with ds-DNA. The extent of the crosslinking reaction, which was complete within 16 mm: (a) reached its maximum at an oligomer concentration of 3 μM; (b) remained constant below the Tin of the duplex and then rapidly decreased; and (c) appeared to depend upon the sequence surrounding the psoralen crosslinking site. An oligomer crosslinked to the template strand inhibited tran scription by T7 RNA polymerase whereas an oligoiner crosslinked to the non-template strand had only a small inhibitory effect. Oligomers did not crosslink to ds-DNA undergoing transcription nor did they inhibit the transcription reaction.
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