Translational efficiency of redundant ACG initiator codons is enhanced by a favorable sequence context and remedial initiation.
Earlier studies showed that the redundancy of ACG initiation codons enhanced the efficiency of translation initiation by 3- to 6-fold. Evidence presented here shows that this "redundancy effect" can be attributed to a favorable sequence context and, to a lesser extent, remedial initiation. In the case of redundant ACG initiator codons, the second ACG not only acts as a remedial initiation site for scanning ribosomes that skip the first ACG but also enhances the activity of the preceding initiator by providing a preferable "A" at its relative +4 position. Hence, non-successive ACG codons can be as effective as successive ACG codons in initiation, if positioned within a similar context. In contrast, redundant GUG initiation codons (GUG/GUG) bear an unfavorable "G" nucleotide at both the +4 and -3 positions relative to the first and second GUGs, respectively, such that redundant GUG codons act more poorly as translation initiation sites than does a single GUG with a favorable "A" nucleotide in the +4 position ( approximately 2.5-fold). Thus, the sequence context plays a much more important role than remedial initiation in modulating the efficiency of translational initiation from redundant non-AUG codons.
Chen
Shun-Jia
SJ
Department of Life Science, National Central University, Jung-li 320, Taiwan.
Ko
Chou-Yuan
CY
Yen
Chih-Wei
CW
Wang
Chien-Chia
CC
D018387:Codon, Initiator / Q000235:genetics*; D008928:Mitochondria / Q000378:metabolism; D009711:Nucleotides / Q000235:genetics; D014176:Protein Biosynthesis / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
D018387:Codon, Initiator; D009711:Nucleotides; D011994:Recombinant Proteins