Both VP2 and VP3 are synthesized from each of the alternative spliced late 19S RNA species of simian virus 40

Good, Peter J.; Welch, R C; Barkan, Alice; Somasekhar, Madhu B.; Mertz, Janet E.

doi:10.1128/jvi.62.3.944-953.1988

Cited by 42 publications

(25 citation statements)

References 55 publications

(49 reference statements)

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“…The scanning model predicts that, upon introducing an adventitious upstream AUG codon (in a good context), initiation should shift to the upstream site. Thus, if an upstream AUG codon is in the wrong reading frame, it should, and does, depress the yield of protein from the normal site (10,39,70,105,144,156,198,214,282). Ira strong AUG codon is introduced upstream from, and in the same reading frame as, the normal initiator codon, the result is a stretched polypeptide with an NH2-terminal amino acid extension.…”

Section: Evidence From Higher Eukaryotesmentioning

confidence: 99%

The scanning model for translation: an update.

Kozak

1989

The Journal of Cell Biology

3,442

104

2,016

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The small (40S) subunit of eukaryotic ribosomes is believed to bind initially at the capped 5'-end of messenger RNA and then migrate, stopping at the first AUG codon in a favorable context for initiating translation. The first-AUG rule is not absolute, but there are rules for breaking the rule. Some anomalous observations that seemed to contradict the scanning mechanism now appear to be artifacts. A few genuine anomalies remain unexplained.

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Section: Evidence From Higher Eukaryotesmentioning

confidence: 99%

The scanning model for translation: an update.

Kozak

1989

The Journal of Cell Biology

3,442

104

2,016

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“…If the NetStart definition of probable translation start sites was strictly used (score of Ͼ0.5), SV40 19S mRNA would contain only a Vp2 and a Vp4 start codon. However, in SV40-infected cells, Vp2 and Vp3 are both made from the 19S mRNA, where Vp3 is synthesized from its own start codon independently from Vp2 (13,14). Contrary to the translation initiation prediction by Daniels and colleagues, the Vp2 start codon has a weaker Kozak sequence than the Vp3 start codon (15), leading to leaky ribosome scanning (13,14).…”

Section: Perspectivementioning

confidence: 90%

“…However, in SV40-infected cells, Vp2 and Vp3 are both made from the 19S mRNA, where Vp3 is synthesized from its own start codon independently from Vp2 (13,14). Contrary to the translation initiation prediction by Daniels and colleagues, the Vp2 start codon has a weaker Kozak sequence than the Vp3 start codon (15), leading to leaky ribosome scanning (13,14). Together with two internal ribosome entry sites upstream of the Vp3 coding sequence, this probably explains the higher expression of Vp3 than of Vp2 seen in SV40-infected cells (16).…”

Section: Perspectivementioning

confidence: 99%

“…There are several examples showing that disturbance of upstream start codons might influence expression. An SV40 mutant producing 19S but not 16S mRNA could produce Vp1 if a large deletion was introduced upstream of the Vp1 start codon or if the Vp3 start codon was mutated (13). Moreover, in vitro translation of SV40 Vp2 was most efficient without an upstream start codon (13).…”

Section: The Proof Of Vp4 Expression After Sv40 Genome Transfectionmentioning

confidence: 99%

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Does the Evidence Support the Existence of the Simian Polyomavirus SV40 Vp4 Viroporin?

Henriksen

Rinaldo

2020

mSphere

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The simian polyomavirus SV40 was reported to express Vp4, an N-terminally truncated form of the minor capsid proteins Vp2 and Vp3. Since a missense mutation of the putative Vp4 start codon (Vp2M228I) was found to give reduced progeny release and delayed lysis, Vp4 was claimed to be a viroporin. However, two independent research groups, including our own, were unable to replicate these findings. In contrast, we found no Vp4 expression in SV40-infected cells and no reduction in progeny release for Vp4-deficient virus, and finally, we found that the single amino acid substitution unavoidably introduced into the overlapping Vp2/Vp3 genes during Vp4 mutagenesis reduced early steps but not virus release. Remarkably, the existence of the viroporin Vp4 still seems to be widely accepted, which presumably is preventing important research on polyomavirus release. With this perspective, we will review and comment on the most important experiments that led to the disputed announcement of the viroporin Vp4.

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“…1]) encodes LP1 as well (1). Each of the 19S mRNA species encode all three virion proteins; however, only VP2 and VP3 are synthesized from these mRNAs (5). Most, if not all, of VP3 synthesis from the 19S mRNAs of SV40 occurs by leaky scanning past the weak VP2 translation initiation signal (UCCAUGG) (2,30).…”

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confidence: 99%

Leader-encoded open reading frames modulate both the absolute and relative rates of synthesis of the virion proteins of simian virus 40

Sedman

Good

Mertz

1989

J Virol

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Numerous viral and cellular RNAs are polycistronic, including several of the late mRNA species encoded by simian virus 40 (SV40). The functionally bicistronic major late 16S and functionally tricistronic major late 19S mRNA species of SV40 contain the leader-encoded open reading frames (ORFs) LP1, located upstream of the sequence encoding the virion protein VP1, and LP1*, located upstream of the sequence encoding the virion proteins VP2 and VP3. To determine how these leader ORFs affect synthesis of the virion proteins, monkey cells were transfected with viral mutants in which either the leader-encoded translation initiation signal was mutated or the length and overlap of the leader ORF relative to the ORFs encoding the virion proteins were altered. The levels of initiation at and leaky scanning past each initiation signal were determined directly by quantitative analysis of the viral proteins synthesized in cells transfected with these mutants. Novel findings from these experiments included the following. (i) At least one-third of ribosomes bypass the leader-encoded translation initiation signal, GCCAUGG, on the SV40 major late 16S mRNA. (ii) At least 20% of ribosomes bypass even the consensus translation initiation signal, ACCAUGG, when it is situated 10 bases from the 5' end on the major late 16S mRNA. (iii)O The presence of the leader ORF on the bicistronic 16S mRNA species reduces VP1 synthesis threefold relative to synthesis from a similar RNA that lacks it. (iv) At least half and possibly all VP1 synthesized from the bicistronic 16S mRNA species is made by a leaky scanning mechanism. (v) LP1 and VP1 are synthesized from the bicistronic 16S mRNA species at approximately equal molar ratios. (vi) Approximately half of the VP1 synthesized in SV40-infected cells is synthesized from the minor, monocistronic 16S mRNA even though it accounts for only 20% of the 16S mRNA present. (vii) The presence and site of termination of translation of the leader ORF on the late 19S mRNAs affect the relative as well as absolute rates of synthesis of VP2 and VP3.

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Both VP2 and VP3 are synthesized from each of the alternative spliced late 19S RNA species of simian virus 40

Cited by 42 publications

References 55 publications

The scanning model for translation: an update.

The scanning model for translation: an update.

Does the Evidence Support the Existence of the Simian Polyomavirus SV40 Vp4 Viroporin?

Leader-encoded open reading frames modulate both the absolute and relative rates of synthesis of the virion proteins of simian virus 40

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