Open AccessInhibition of T7 RNA Polymerase Transcription by Phosphate and Phosphorothioate Triplex‐Forming Oligonucleotides Targeted to a R · Y Site Downstream from the Promoter
Author(s) -
AlunniFabbroni Marianna,
Manfioletti Guidalberto,
Manzini Giorgio,
Xodo Luigi E.
Publication year - 1994
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1994.00831.x
Subject(s) - t7 rna polymerase , transcription (linguistics) , oligonucleotide , microbiology and biotechnology , rna polymerase , pyrimidine , chemistry , rna polymerase ii , polymerase , rna , transcription bubble , biology , dna , promoter , stereochemistry , biochemistry , bacteriophage , gene , gene expression , linguistics , philosophy , escherichia coli
The effect of triplex‐forming oligonucleotides (TFO) on the transcription activity of T7 RNA polymerase has been investigated by an in vitro assay. The TFOs, either containing only phosphate (PO 2 ) or phosphate and phosphorothioate (POS) internucleotide linkages, were targeted to a 30‐bp homopurine · homopyrimidine (R · Y) site cloned in plasmid Bluescript KS+ about four helical turns downstream from the T7 RNA promoter. Band‐shift and ultraviolet absorption melting experiments showed that the designed pyrimidine PO 2 and POS TFOs form stable triple‐helical complexes with the R · Y target duplex (the Δ G TFO values of triplex formation vary from –42 to –63 kJ/mol). The triple‐helical complexes resulting from POS oligonucleotides were less stable (by 4–12 kJ/mol) than those obtained with PO 2 analogues, the magnitude of destabilization being dependent on the number of POS groups present in the third strand. The designed TFOs were shown to efficiently repress bacteriophage T7 RNA polymerase transcription under different experimental conditions. The repression depended on pH, TFO concentration and temperature. When the TFO/template ratio was fixed to 100, a strong repressive effect was observed with normal and phosphorothioate pyrimidine TFOs, also under physiological conditions. In contrast, a purine‐rich oligonucleotide containing 44% of guanine residues promoted only a weak transcription inhibition, even at a TFO/template ratio as high as 750. Both PO 2‐ and POS‐containing pyrimidine TFOs produced their strong repressive effect on T7 RNA polymerase transcription even when they were added to the reaction mixture simultaneously with the polymerase. A mechanism of transcription repression is discussed. The data reported in this paper are useful for designing oligonucleotides acting as artificial repressors in the antigene strategy and indicate that the R · Y target need not to be precisely confined to the promoter.