The description of the protein encoded in this ORF: c-myc proto-oncogene, isoform c-myc2(AUG translation initiation codon), 64 kDa.
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): 396-1955
This is the sequence encoding mRNA transcribed from major P2 promotor. P2 mRNA encodes two proteins of 67 and
64 kDa in size designated c-myc1 and c-myc2 respectively:
- c-myc1 is produced when alternative initiation of translation starting at non-canonical CUG codon occurs
- c-myc2 is translated from conventional AUG codon protein represents prevalent isoform of c-myc in mammalian
Nanbru et al., 1997 have used bi- and tri-cistronic constructs to study c-myc IRES. The two internal TATA
boxes present in c-myc UTR were masked by directed mutagenesis. Integrity of the transcripts was tested by
Northern blot. Also T7 in vitro transcripts and rabbit reticulocyte lysates were used to demonstrate IRES
activity. They conclude IRES position between -363 and -94b upstream the CUG initiation codon.
Integrity of the transcripts from pGL3Rutr transfected HeLa cells was tested by RNase protection assay. The
protected fragment contained 64b from 3'-end of Rluc, 447b of the intercistronic region and 101b from the
5'-end of Fluc. No direct RNA transfection performed or in vitro translation or promoter-less plasmid used to
test cryptic promoter presence (Stoneley et al., 1998).
Johannes et al., 1998 have shown that c-myc is associated with polysomes during poliovirus infection and that
the protein is actually being synthesized.
Stoneley et al., 2000 reported that in vaccinia virus infected human TK143 cells expressing T7 polymerase the
c-myc IRES is not functional due to the lack of "nuclear experience". Further, c-myc IRES in capped GpppG
bicistronic run-off transcripts with poly(A) of length 30 was not functional either. They have also shown in
Figure 2 that the IRES is most active in HeLa cells, with decreasing activity in MRC5, HepG2, GM637, HK293,
COS7, MCF7, Balb/c 3T3, MEL cell lines. Finally, it was concluded that c-myc IRES requires a non-canonical
translation initiation cofactor like entero- and rhinovirus IRESs and unlike cardio- and aphtovirus IRESs
(as originally reported by Borman et al. (1997), Nucleic Acids Res. 25:925-932).
Subkhankulova et al., 2001 studied effect of various stresses on c-myc and Apaf-1 IRES activity.
Creancier et al., 2001 have shown the activity of pRF based plasmids containing c-myc IRES in many cell lines
and embryonic/adult mouse tissues (c-myc IRES found inactive in adult tissues).
Kim et al., 2003 have shown that hnRNP C1 stimulates the IRES activity through its binding to internal polyU
sequence. hnRNP C1 also stimulates in a dose dependent manner translation from a downstream cistron (FFluc) in
rabbit reticulocyte lysate.
Shi et al., 2005 tested c-myc in pRF promoter-less plasmids (SV40 promoter deleted) and integrity of the
transcripts by Northern blot. T7 transcripts poorly translated in rabbit reticulocyte lysates.
Bert et al. (2006) tested c-myc IRES in HeLa cells using promoter-less plasmids with or without the enhancer
left in (Figure 2). They showed there is a cryptic promoter activatable when the enhancer is left in.
The IRES absolute position (the range includes START and STOP codons or their equivalents): 1-393
How IRES boundaries were determined: experimentally_determined
The sequence of IRES region aligned to its secondary structure (if available):
1-393 base range has comparable IRES activity to 1-340 region. Further deletions of 1-340 region result in
lower IRES activity. Please note that the very last 2 bases of 5'-UTR were not cloned into the pGL3Rutr alias
pRMF vector to keep the putative IRES 'in frame' with the initiator ATG codon (Evans et al. (2003), Fig. 1B
legend) while they have been replaced by 'cc' of NcoI site 'ccATGg'.
Bert et al. (2006) reported c-myc IRES is only 3x more functional than a negative control while EMCV IRES was
221x in direct RNA transfection (Figure 4).
Andreev et al. (2009) objected existence of the c-myc IRES.