Secondary Structure and the Role in Translation Initiation of the 5′-Terminal Region of p53 mRNA

Abstract

The p53 protein is one of the major factors involved in cell cycle control, DNA repair, and induction of apoptosis. We determined the secondary structure of the 5'-terminal region of p53 mRNA that includes two major translation initiation codons AUG1 and AUG2, responsible for the synthesis of p53 and its N-truncated isoform ΔN-p53. It turned out that a part of the coding sequence was involved in the folding of the 5' untranslated region for p53. The most characteristic structural elements in the 5'-terminal region of p53 mRNA were two hairpin motifs. In one of them, the initiation codon AUG1 was embedded while the other hairpin has been earlier shown to bind the Mdm2 protein. Alternative mechanisms of p53 mRNA translation initiation were investigated in vitro using model mRNA templates. The results confirmed that initiation from AUG1 was mostly cap-dependent. The process was stimulated by a cap structure and strongly inhibited by a stable hairpin at the template 5' end. Upon inhibition, the remaining protein fraction was synthesized in a cap-independent process, which was strongly stimulated by the addition of a cap analogue. The translation initiation from AUG2 showed a largely cap-independent character. The 5' cap structure actually decreased initiation from this site which argues against a leaky scanning mechanism but might suggest the presence of an IRES. Moreover, blocking cap-dependent translation from AUG1 by the stable hairpin did not change the level of initiation from AUG2. Upon addition of the cap analogue, translation from this site was even increased.

Characterization of Arabidopsis FPS Isozymes and FPS Gene Expression Analysis Provide Insight into the Biosynthesis of Isoprenoid Precursors in Seeds

“…These observations suggested that translation of the chimeric FPS2::FPS1S mRNA expressed by FPS2p::FPS1S was severely impaired, which is most likely due to the different structural environment around the AUG start codon of the FPS2::FPS1S mRNA compared to that of the FPS2 and FPS2::FPS1S-mutdis mRNAs (Figure S1). Among the different structural features known to be involved in translational control of specific mRNAs [53], base-pairing involving nucleotides within the AUG codon has been recognized as an important structural determinant that may influence translation initiation [54], [55].…”

Alternative Mechanisms to Initiate Translation in Eukaryotic mRNAs

“…In mRNAs subjected to polyamine-responsive translation regulation, uORFs act as sensors of polyamine levels [10]. Finally, in many other mRNAs, uORFs are obstacles that block or delay scanning ribosomes causing a strong reduction of protein synthesis, as exemplified in the 5′ terminal region of p53 mRNA or the embryonic form of the chicken proinsulin mRNA [5, 6]. …”

Structure of Ty1 Internally Initiated RNA Influences Restriction Factor Expression

“…The structural context of the AUG codon can modulate translation efficiency [27]. Coding sequences can also participate in the folding of the 5′ untranslated regions that modulate RNA stability [28,29]. However, coding sequence contributions to translation initiation remain understudied since functional and structural characterization is usually conducted on isolated 5′ UTR sequences.…”