The yeast transcription factor genes YAP1 and YAP2 are subject to differential control at the levels of both translation and mRNA stability

Abstract

Two forms of post-transcriptional control direct differential expression of the Saccharomyces cerevisiae genes encoding the AP1-like transcription factors Yap1p and Yap2p. The mRNAs of these genes contain respectively one (YAP1 uORF) and two (YAP2 uORF1 and uORF2) upstream open reading frames. uORF-mediated modulation of post-termination events on the 5'-untranslated region (5'-UTR) directs differential control not only of translation but also of mRNA decay. Translational control is defined by two types of uORF function. The YAP1 -type uORF allows scanning 40S subunits to proceed via leaky scanning and re-initiation to the major ORF, whereas the YAP2 -type acts to block ribosomal scanning by promoting efficient termination. At the same time, the YAP2 uORFs define a new type of mRNA destabilizing element. Both post-termination ribosome scanning behaviour and mRNA decay are influenced by the coding sequence and mRNA context of the respective uORFs, including downstream elements. Our data indicate that release of post-termination ribosomes promotes largely upf -independent accelerated decay. It follows that translational termination on the 5'-UTR of a mature, non-aberrant yeast mRNA can trigger destabilization via a different pathway to that used to rid the cell of mRNAs containing premature stop codons. This route of control of non-aberrant mRNA decay influences the stress response in yeast. It is also potentially relevant to expression of the sizable number of eukaryotic mRNAs that are now recognized to contain uORFs.

Constitutive and Nitrogen Catabolite Repression-sensitive Production of Gat1 Isoforms

“…Such regulatory events have been documented with respect to controlled production of DNA-binding proteins (60) or in response to environmental cues or stresses (61,62). However, in the absence of further evidence, we cannot favor one of the above possibilities over another to explain why Gat1 Met-1 could not be demonstrated to function and how two or perhaps three isoforms differing in their N termini are produced in vivo.…”

Endless possibilities: translation termination and stop codon recognition

“…While the mechanism of action of these cis sequences is not fully understood, it is clear that no single sequence confers these properties, and that a wide variety of contexts can achieve the same effect (Grant & Hinnebusch, 1994). uORFs in the 5h UTRs of the YAP1 and YAP2 genes, while having different sequences surrounding their stop codons, nevertheless have very similar properties to GCN4 uORFs 1 and 4, respectively, again an indication that primary sequence itself is not the prime determinant of the ability to promote resumed scanning (Vilela et al, 1998). It has been suggested that the GC-rich environment around the uORF4 stop codon may pause a terminating ribosome (perhaps via rRNA interaction) long enough to allow a putative recycling factor to bind, an event prevented by rapid termination at uORF1 (Grant & Hinnebusch, 1994).…”

In-depth analysis of cis-determinants that either promote or inhibit reinitiation on GCN4 mRNA after translation of its four short uORFs

“…REI is a gene-specific regulatory mechanism exploiting the presence of short upstream uORFs in mRNA leaders (i.e., 5 ′ untranslated regions-5 ′ UTRs) of various genes. The molecular key to this potentially abundant regulation (Davuluri et al 2000;Iacono et al 2005;Calvo et al 2009;Hood et al 2009;Zhou et al 2010) is the ability of some of these short uORFs (in yeast up to five codons in length [Vilela et al 1998;Rajkowitsch et al 2004;Szamecz et al 2008], in plants up to 16 [von Arnim et al 2014], and in mammals up to 30 codons [Kozak 2005]) to retain the 40S ribosomal subunit on the same mRNA molecule even after they have been translated and the large 60S subunit has been recycled by the ribosome recycling factors (for review, see Jackson et al 2012;Valášek 2012). Such post-termination 40S subunits are then able to resume scanning downstream, and upon acquisition of the new ternary complex (TC), composed of MettRNA i Met and eukaryotic initiation factor eIF2 in its GTP form, they are able to recognize the AUG start codon of the next ORF and reinitiate translation thereon.…”