IRESite record type: plasmid_with_promoter_and_putative_IRES_without_translational_characterization
The shape of the nucleic acid molecule translated: linear
The quality of the mRNA/+RNA sequence: hopefully_full-length_mRNA
The mRNA/+RNA description:
Bicistronic T7 capped mRNA transcript used for in vitro translation (with short synthetic polyA tail (35nt
only)). It includes stable RNA hairpin deltaG = -60 kcal/mol inserted at unique NheI immediately upstream
RLuc.
The mRNA/+RNA sequence represented in the +DNA notation:
Credibility of mRNA sequence: end-to-end_sequence_completely_same_as_in_the_experiment
The IRES absolute position (the range includes START and STOP codons or their equivalents): 1105-2242
How IRES boundaries were determined: experimentally_determined
5'-end of IRES relative to last base of the STOP codon of the upstream ORF: 16
3'-end of IRES relative to last base of the STOP codon of the upstream ORF: 1153
5'-end of IRES relative to first base of the START codon of the downstream ORF: -1138
3'-end of IRES relative to first base of the START codon of the downstream ORF: -1
The sequence of IRES region aligned to its secondary structure (if available):
Remarks:
IRES activity as shown in Fig. 2. in this construct cannot be interpreted as there was no correct positive nor
negative control. In vitro transcripts were produced using T7 polymerase in presence of m7G cap analog at
ratio of 4:1 versus rGTP and equimolar amounts of RNA were subject to translation in RRL. RNAs had short
(35nt) long polyA tail. The yields from the first cistron were not equal although all transcripts were capped
and 5'-UTRs had same length. One of the possible explanations might be that different efficiencies of capping
account for this. One could have few concerns: 1) a plasmid phpRL-FL should have been employed as the negative
control. Unfortunately, such plasmid was not even constructed. 2) Similarly, no phpRL-HCV-FL was
employed&constructed as the tempting positive control. Thus, the only conclusion is that the hairpin structure
(-60 kcal/mol, 143 bp insert size containing the hairpin while we did not verify (using mfold) whether the
actual hairpin spans the whole region or only its part) decreases translation from the first cistron by 98%
and that lowering cap-dependent initiation also results in lower IRES-dependent yields from the second
cistron. The hairpin insert is separated by 4 nt from the initiator ATG of RLuc.