It has been suggested previously that termination-reinitiation is dependent on the stop codon of the uORF and the start codon of the downstream ORF lying in close proximity [8, 11, 15, [17] [18] [19] 32, 33] . Indeed, movement of the M1 stop codon more than 24 nt downstream of its original context in the terminationreinitiation 'window' of the BM2 signal results in inhibition of reinitiation on the BM2 ORF [11] . However, in all previous investigations into proximity effects of the start and stop codons, the termination site was moved downstream of the start codon of the upstream ORF [8, 11, 15, [17] [18] [19] 32] ). Given that terminationreinitiation almost certainly depends on interactions between the terminating ribosome and the TURBS, it is conceivable that these experiments have overestimated the importance of the relative proximity of the stop and start codons and that the distance between the terminating ribosome and the TURBS is the crucial issue. To investigate this, a series of mRNAs were prepared in which the UAAUG overlap was moved downstream en masse such that the distance between the stop and start codons was conserved but the ribosome would terminate at varying distances relative to the TURBS ( Figure 5B) . A series of control mRNAs were also examined in which the stop codon alone was shifted downstream of the BM2 start codon ( Figure 5A ; details in [11] ). In all constructs, nucleotides at -3 and +4 relative to the BM2fluc AUG were maintained to control for context effects of the start codon. As observed previously in the control series [11] , reinitiation occurred efficiently when the stop codon was moved up to 24 nt downstream of its original placement but was abolished when the stop was moved further ( Figure 5A ). Importantly, BM2 translation The 44 kDa product produced from this mRNA corresponds to the rlucM1 product, the 62 kDa product is the BM2fluc reinitiation product. The molar excess of AON (oligo) in relation to the mRNA is shown above the autoradiograph. (B) The sequence upstream of the termination-reinitiation site (UAAUG) is shown, with the A residue at the start of the TURBS underlined. Also shown is the core sequence of motif 1 in bold. The regions targeted followed the same pattern in mRNAs where the UAAUG motif was moved as a unit, with ablation of synthesis observed when this sequence was moved any further than 24 nt downstream of its original site ( Figure 5B) . These experiments reveal that the placement of the 40S subunit relative to the TURBS, posttermination, is quite critical.