Attenuation May Regulate Gene Expression in Animal Viruses and Cell

Regulation of eukaryotic gene expression by transcriptional attenuation.

“…The first demonstrations of transcriptional attenuation in eukaryotes emerged from analysis of RNAs expressed from the SV40-and adeno-viruses in infected animal cells (Laub et al, 1980;Hay et al, 1982;Aloni and Hay, 1985). SV40 late transcription was shown to terminate prematurely at a site 95 nucleotides (nt) downstream from the promoter when analyzed in either isolated nuclei or SV40 viral transcription complexes.…”

The block to transcription elongation at the minute virus of mice attenuator is regulated by cellular elongation factors.

“…To do so, following pulse-labeling for 1 shows the structure of the template DNA and the expected lengths of the runoff and attenuator RNAs). Figure 1A shows that the 142-to 147-nt MVM attenuator RNA was produced when KCl concentrations higher than 0.2 M were used in the elongation reaction.…”

“…The virus was allowed to absorb for 2 h, and then the culture was diluted back to 1 liter Runcvt; 21 5 FIG. 1 Partial purification of transcription complexes by Sephacryl S-1000 chromatography. The preinitiation step as described above was used but at eight times the volume; 500 puM ATP, CTP, and GTP and 240 puCi of [ot-32P]UTP were added for 1.5 min at 30°C, and then 320 pI of the reaction mixture was applied to a Sephacryl S-1000 minicolumn (4-ml volume) that has been equilibrated with 300 mM KCI-20 mM Tris-HCI (pH 7.9)-5 mM MgCl2-0.1 mM EDTA-7.5% glycerol-1 mM dithiothreitol.…”

“…The general transcription factors IIF and UX were also shown to alleviate this block to transcription elongation. On the basis of these results, we suggest that the block to elongation at the MVM attenuation site observed late in MVM infection results, at least in part, from the inactivation of the general transcription elongation factors.Recently, it has been shown that eukaryotic RNA polymerase II, like the prokaryotic polymerase, can pause or terminate both in vivo and in vitro transcription within viral (1,3,16,17,19,24,28,29,32,38) and cellular (4,8,9,15,18) genes and thus modulate downstream gene expression. This mechanism is termed attenuation (39).…”

“…To date, however, little is known about cis and trans elements involved in the attenuation mechanism in eukaryotes. We have shown that at least in some viral systems, RNA polymerase II can respond to a stem-loop structure in the RNA followed by polyuridines as a signal for the elongation block in vitro (1,3,16,19,28,29,32). In other systems, different sequences constitute the attenuation signal (2,9,31,34,40).…”