The block to transcription elongation at the SV40 attenuation site is decreased in vitro by oligomers complementary to segments of the attenuator RNA.

We have previously reported that a mechanism resembling attenuation in prokaryotes regulates simian virus 40 (SV40) late gene expression. We have suggested that modulation of the attenuator RNA secondary structure is an integral element regulating the elongation block at the attenuation site [Hay et al., Cell 29 (1982) 183-193]. In the present study, oligodeoxyribonucleotides (oligos), 13-19 nucleotides long, were used to probe the involvement of the attenuator RNA secondary structure in the control of elongation block at the SV40 attenuation site. These oligos are complementary to segments of the attenuator RNA suggested to play a role in the regulation of attenuation. The oligos were added to an in vitro transcription reaction containing SV40 transcription complexes, and their effect on transcription through the attenuation site was measured. As predicted, the three oligos caused specific decreases in the elongation block at the SV40 attenuation site. These results provide direct evidence for the involvement of RNA secondary structure in the attenuation mechanism in SV40.