The description of the protein encoded in this ORF: Heat shock protein 83 CG1242-PA
The translational frameshift (ribosome slippage) involved: 0
The ribosome read-through involved: no
The alternative forms of this protein occur by the alternative initiation of translation: no
The ORF absolute position (the base range includes START and STOP codons or their equivalents): 342-2495
Remarks:
The cloned 5'-UTR by Ahmed, R. and Duncan, R.F.(2004) was not the entire 5'-UTR. Nucleotide number one
published by them is the 193rd nucleotide according to GI:24656565. The sequence gene model can be confirmed
by EST records GI:13698172, GI:13689118, GI:13684254, GI:3102337, GI:114073046 (the last EST contains also the
poly(A) region).
The IRES name: Hsp90 Warning: please make ires_name same as the gene_name and optionally append to it coordinates. E.g. when gene/virus name is EMCV-R use EMCV-R_-222_to_-1 or EMCV-R_1-456, etc. but not Emcv-R-... or EMCV-222_to_-1. Please keep case of letters as well. This rewards when searching through the database.
The IRES absolute position (the range includes START and STOP codons or their equivalents): 193-341
Conclusion: unproved_IRES
How IRES boundaries were determined: experimentally_determined
The sequence of IRES region aligned to its secondary structure (if available):
Remarks:
Possibility of IRES-mediated translation was tested under normal and heat-shock conditions in Drosophila
melanogaster S2 cells. If at all, IRES activity was confirmed only in the heat shock conditions while under
normal circumstances the cap-dependent translation driven by eIF4E (and sensitive to the eIF4E-BP
overexpression) is prevalent. However, authors did not state clearly there is IRES activity at all.
The rate of synthesis of Hsp90 protein (Fig. 1A) was increased by heat shock. The biggest increase was noticed
when the temperature raised from 29 to 35 °C and from 35 to 37 °C the protein synthesis decreased.
Actinomycin D treatment (Fig. 1) which blocks transcription was used to study efficiency of translation of
various Hsp mRNAs (Hsp90, Hsp70, Hsp26/28, Hsp22/23) in Drosophila S2 cells. With increasing heat shock the
amount of radiolabeled Hsp90 proteins newly translated increased whereas amounts of Hsp70, 26/28 and 22/23
proteins decreased. It has been concluded that some of 5'-UTRs mediate more efficiently translation of their
respective messages.
No bicistronic mRNA tests were employed at all, no positive control containing known IRES has been used, and
neither direct RNA transfection was performed nor T7 polymerase-based cytoplasmic transcription was used to
prove the special advantage of Hsp90 5'-UTR is due to IRES.
Overexpression of eIF4E-BP (Fig. 5) reduced the translation of Hsp90 by >95% under normal growth temperature
(22-24 °C) whereas during heat shock (36 °C, 15 min) overexpression of eIF4E-BP inhibited Hsp90 IRES
activity to ~60% only.
Authors confirmed that Drosophila eIF4E-BP is dephosphorylated during heat shock and therefore is expected to
be able to bind eIF4E (Fig. 6). These results say that it is concerned about cap-dependent translation.
In figure 8 various deletions of the incomplete 5'-UTR showed that the region 77-149 nt (269-341 region of the
complete 5'-UTR of GI:24656565 annotated here in IRESite) confers at least some translation advantage during
heat shock. But, it is unclear whether this is due to a stable secondary structure which melts during heat
shock or whether it is contributed (even in part) by IRES. In this experiment, Drosophila S2 cells were
transfected by a metalothionein promoter-driven expression plasmid MT90-FL (metallothionein-promoter ->
Hsp90 5'-UTR (193-341 of GI:24656565)-> "internally deleted" Hsp70 coding region containing only 44kDa region
of Hsp70 -> Hsp70 3'-UTR) expressing 44kDa protein (Hess and Duncan, 1996). In the legend this figure 8
authors say that translation rate equals translational efficiency which is supported by Northern analysis
(data not shown).
natural_transcript