Positive and negative control of translation by the leader sequence of cauliflower mosaic virus pregenomic 35S RNA.

Abstract

We have studied the influence of the 600 nt long leader sequence of cauliflower mosaic virus 35S RNA on downstream translation. Plant protoplasts were transfected with plasmids expressing a CAT reporter gene from a mRNA, containing wild‐type or mutant forms of the 35S RNA leader. Deletion analysis revealed the presence of three separate stimulatory sequence regions, S1, S2 and S3. The latter two interact with each other to enhance downstream translation 5‐ to 10‐fold. This enhancement was not observed in protoplasts from a non‐host plant. In the absence of either S2 or S3, the region I2, located in between, exerts an inhibitory effect on downstream translation, probably due to the presence of short open reading frames. Expression of a reporter gene inserted into I2 increases 2‐fold upon deletion of either S2 or S3. We propose that mRNA regions S2 and S3 form a complex with cellular factors that allows scanning ribosomes to bypass region I2.

Continuous and Discontinuous Ribosome Scanning on the Cauliflower Mosaic Virus 35 S RNA Leader Is Controlled by Short Open Reading Frames

“…A second alternative to the linear scanning route is a ribosome shunt, as shown for the RNAs of Sendai virus (12,13), cauliflower mosaic virus (CaMV) (14,15), rice tungro bacilliform virus (16), adenovirus (17,18), and papillomavirus (19). The shunt process allows ribosomes to bypass RNA regions that may include AUG codons and secondary structures inhibiting linear migration (for review, see Ref.…”

“…It does not function as an internal ribosome entry site when placed between two cistrons (22). Expression downstream of the 35 S RNA leader occurs via ribosome shunt, which requires three cis elements within the leader, a capped 5Ј end (14,23), a 5Ј proximal sORF (sORF A; 4 codons in length), and, following it after 6 nt, a stable stem (stem section 1) (22,24,25). The translation event at the sORF is needed for efficient shunting (26,27).…”

“…The elongated hairpin structure promotes shunting by bringing the shunt "take off" and "landing" sites into close spatial proximity (15,22). Shunting does not require viral or specific host factors, because it functions in plant protoplasts, wheat germ extract, and reticulocyte lysate (14,23,26), but it can be enhanced by a CaMVencoded transactivator protein (27).…”

Mechanism of ribosome shunting in Rice tungro bacilliform pararetrovirus

“…This unusual initiation process has been first discovered in Cauliflower mosaic virus (CaMV) (Fü tterer et al 1990(Fü tterer et al , 1993 and then in Ricet ungro bacilliform virus (RTBV) (Fü tterer et al 1996), both belongingt op lant pararetroviruses. Similar phenomenah ave laterb een described for several animal viruses, including Sendai paramyxovirus (Latorree ta l. 1998;d eB reynee ta l. 2003), human typeCadenovirus (Yueh andSchneider 1996, 2000;Xi et al 2004), human papillomavirus (Remm et al 1999), and duck hepatitis Bp araretrovirus ( Sen et al 2004), and for some cellular mRNAs( Yueha nd Schneider 2000; Rogers et al 2004).…”

Cauliflower Mosaic Virus Gene VI Controls Translation from Dicistronic Expression Units in Transgenic Arabidopsis Plants.

“…The translation mechanism from this unusual mRNA has been studied in CaMV and figwort mosaic virus (another member of the caulimovirus group) by isolating and testing polar mutants and their revertants (Sieg and Gronenborn, 1982;Dixon and Hohn, 1984) and by expressing CaMV derivatives in vitro (Gordon et al, 1988) and in plant protoplasts Fütterer et al, 1988Fütterer et al, , 1989Fütterer et al, , 1990aFütterer et al, , 1990bBonneville et al, 1989;Gowda et al, 1989;Fütterer and Hohn, 1991;Scholthof et al, 1992). In summary, the results suggest that the translational machinery starts scanning at the cap site To whom correspondence should be addressed.…”