INVESTIGATION OF SOME PROPERTIES OF OLIGODEOXYNUCLEOTIDES CONTAINING 4'-THIO-2'-DEOXYNUCLEOTIDES - DUPLEX HYBRIDIZATION AND NUCLEASE SENSITIVITY

The thermal stabilities of the duplexes formed between 4'-thio-modifie d oligodeoxynucleotides and their DNA and RNA complementary strands we re determined and compared with those of the corresponding unmodified oligodeoxynucleotides. A 16mer oligodeoxynucleotide containing 10 cont iguous 4'-thiothymidylate modifications formed a less stable duplex wi th the DNA target (Delta T-m/modification -1.0 degrees C) than the cor responding unmodified oligodeoxynucleotide. However, when the same oli godeoxynucleotide was bound to the corresponding RNA target, a small i ncrease in T-m was observed (Delta T-m/modification +0.16 degrees C) w hen compared with the unmodified duplex, A study to identify the speci ficity of an oligodeoxynucleotide containing a 4'-thiothymidylate modi fication when forming a duplex with DNA or RNA containing a single mis match opposite the modification found the resulting T(m)s to be almost identical to the wild-type duplexes, demonstrating that the 4'-thio-m odification in oligodeoxynucleotides has no deleterious effect on spec ificity. The nuclease stability of 4'-thio-modified oligodeoxynucleoti des was examined using snake venom phosphodiesterase (SVPD) and nuclea se S1. No significant resistance to degradation by the exonuclease SVP D was observed when compared with the corresponding unmodified oligode oxynucleotide. However, 4'-thio-modified oligodeoxynucleotides were fo und to be highly resistant to degradation by the endonuclease S1. It w as also demonstrated that 4'-thio-modified oligodeoxynucleotides elici t Escherichia coli RNase H hydrolysis of the RNA target only at high e nzyme concentration.