substitution producing structural changes in the c-myc IRES resulted in increased translation initiation by internal ribosome entry and was associated with oncogenesis (59). SNP rs563649 is located in the IRES loop II, where the major allele C likely allows a better base pairing between loops II and III (AAC:GUU) than the minor allele T (AAU:GUU) (Fig. 3A). To examine effects of rs563649 allelic variants on translation efficiency, we transiently transfected human neuroblastoma BE2C cells with reporter constructs that carried allelic variants of MOR-1K IRES inserted between transcription and translation start sites (Fig. 3B). Similar to the published report (59), the T allelic variant of MOR-1K IRES showed significantly higher translational activity than the C allelic variant (Fig. 3). As the T allelic variant also produced lower mRNA levels (Fig. 3C), these results suggest reciprocal allelic regulation of MOR-1K at the RNA and protein levels, where the T allele leads to increased translational activity, through the increased ribosome binding and the C allele provides higher RNA levels, probably due to decreased accessibility for nucleases.
