Inhibition of in vitro and ex vivo translation by a transplatin-modified oligo(2′-O-methylribonucleotide) directed against the HIV-1 gag-pol frameshift signal

A 2′-O-methylribooligonucleotide containing a G1·U·G3 triad modified by trans-diamminedichloro-platinum(II) was targeted to the RNA region responsible for the gag–pol frameshifting during translation of the HIV-1 mRNA. The binding of the platinated oligonucleotide to its target RNA induced a rearrangement of the (G1,G3)-intrastrand crosslink, leading to the formation of an intermolecular oligonucleotide–RNA G–A crosslink. This resulted in the selective arrest of translation of a luciferase gene placed downstream of the HIV-1 frameshift signal both in a cell-free extract (rabbit reticulocyte lysate) and in RNA-transfected cells. A specific inhibition of luciferase activity was still observed when the oligonucleotide–RNA complex was not pre-formed prior to either translation or transfection. Moreover, a selective inhibition was also observed when the oligonucleotide and the plasmid DNA encoding the luciferase and bearing the RNA gag–pol frameshifting signal were co-transfected in NIH 3T3 cultured cells. Therefore the intrastrand→interstrand conversion of the platinum crosslink kinetically competes with the translation machinery and blocks the polypeptide elongation. These transplatin-modified oligonucleotides which operate within a live cell on a ‘real-time’ basis and do not need an external triggering signal constitute a promising new class of selective reactive probes.