Human RNA Polymerase II Can Prematurely Terminate Transcription of the Adenovirus Type 2 Late Transcription Unit at a Precise Site That Resembles a Prokaryotic Termination Signal

Premature termination of transcription has been demonstrated by eukaryotic RNA polymerase II at specific sites in the major late transcriptional unit of SV40 and in one of the transcriptional units of the parvovirus, minute virus of mice (MVM) (Y. Aloni and N. Hay, CRC Critical Reviews of Biochem., 18:327-383, 1985). In both cases the prematurely terminated (attenuated) RNA can be folded into a hairpin structure followed by U-residues that resemble a termination signal in prokaryotes. The experiments presented herein demonstrate premature termination of transcription 185 nucleotides (nt) downstream from the major late promoter of adenovirus type 2 (Ad2) in vivo, and in vitro in isolated nuclei and in HeLa whole cell extract. As in SV40 and MVM the attenuated RNA of Ad2 can be folded into a hairpin structure followed by U-residues. Transcription-termination was significantly reduced when ITP replaced GTP and when Br-UTP replaced UTP in the transcription reaction mixture, indicating that RNA secondary structure and the rU-dA interactions, respectively, are parts of the termination signal. Moreover, in isolated nuclei transcription-termination at the attenuation site occurred when the reaction mixture contained between 50-150 mM NaCl but not when it contained 300 mM NaCl. These results indicate that, at least in isolated nuclei, attenuation can be regulated. The possible involvement of termination factor(s) in the regulation of attenuation is discussed.