Translation inhibition by an mRNA coding region secondary structure is determined by its proximity to the AUG initiation codon

In the present study we investigate the impact of highly stable coding region secondary structures on mRNA translation efficiency. By introducing antisense segments into the 3′ non-translated region of human α-globin mRNA we are able to synthesize a series of transcripts in which site-specific secondary structures are introduced without altering the primary structure of the 5′ non-translated region, the coding region, or the encoded protein product. Coding region duplexes in close proximity to the AUG initiation codon are found to inhibit translation severely to a degree equal to that of a duplex that extends into the 5′ non-translated region. In contrast, mRNAs containing duplexes positioned further 3′ in the coding region translate at levels that are significantly higher although are still below those of native α-globin mRNA. The primary determinant of translation inhibition by coding region duplexes appears to be the proximity of the duplex to the AUG initiation codon and reflects a parallel inhibition of monosome formation. These data demonstrate that extensive coding region secondary structures suppress translation to a minimal or to a substantial degree depending on their distance from the initiation codon.