Initiation of translation at CUG, GUG, and ACG codons in mammalian cells.
Site-directed mutants of the ACG start codon of the C' protein encoded in the polycistronic Sendai virus P/C mRNA revealed that CUG, GUG, and ACG codons initiated translation rather efficiently (10-30% of the AUG initiation) in COS-1 host cells. In addition, AUA and AUU codons initiated translation at about 5% efficiency, while UUG did not initiate translation. The sequence context of these start codons (purine residues at -3 and +4) was crucial in their recognition by the ribosome. The location of the non-AUG codons in the P/C mRNA did not play a role in its recognition by ribosomes. By using CUG, the most efficient non-AUG start codon, instead of the original ACG codon and inserting an additional upstream CUG codon in the P/C mRNA, the amount of the C' protein was increased and a novel protein was synthesized. Syntheses of an increased level of C' and the novel protein did not affect downstream initiations of the P and C proteins, suggesting that more ribosomes bind the mRNA than are actually utilized for initiation of translation.
Mehdi
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Department of Immunology/Microbiology, Rush-Presbyterian-St. Luke's Medical Center, Chicago, IL 60612.
Ono
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Gupta
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KC
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D003062:Codon; D016297:Mutagenesis, Site-Directed; D010222:Parainfluenza Virus 1, Human / Q000235:genetics*; D011233:Precipitin Tests; D014176:Protein Biosynthesis; D012367:RNA, Viral / Q000235:genetics; D012270:Ribosomes / Q000378:metabolism
D003062:Codon; D012367:RNA, Viral