The DNA of mammalian cells treated with 4,5
,8-trimethylpsoralen (Trioxsalen) is crosslinked (preventing transcription) only after photoactivation with near ultraviolet light. Suppression of gene action in cocultivated or fused cultures, including both induction and antiviral action of fibroblast interferon, can consequently be limited to pretreated cells, an advantage over actinomycin treatment.
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