Predicted RNA Binding Proteins Pes4 and Mip6 Regulate mRNA Levels, Translation, and Localization during Sporulation in Budding Yeast

Abstract

In response to starvation, diploid cells of undergo meiosis and form haploid spores, a process collectively referred to as sporulation. The differentiation into spores requires extensive changes in gene expression. The transcriptional activator Ndt80 is a central regulator of this process, which controls many genes essential for sporulation. Ndt80 induces ∼300 genes coordinately during meiotic prophase, but different mRNAs within the regulon are translated at different times during sporulation. The protein kinase Ime2 and RNA binding protein Rim4 are general regulators of meiotic translational delay, but how differential timing of individual transcripts is achieved was not known. This report describes the characterization of two related -induced genes, and , encoding predicted RNA binding proteins. These genes are necessary to regulate the steady-state expression, translational timing, and localization of a set of mRNAs that are transcribed by but not translated until the end of meiosis II. Mutations in the predicted RNA binding domains within alter the stability of target mRNAs. and affect only a small portion of the regulon, indicating that they act as modulators of the general Ime2/Rim4 pathway for specific transcripts.

Mip6 binds directly to the Mex67 UBA domain to maintain low levels of Msn2/4 stress‐dependent mRNAs

“…To gain insights into the cellular role of Mip6, we investigated whether Mip6, similar to Mex67, shuttles between the nucleus and the cytoplasm. Unfortunately for the purpose of such analysis, an endogenous Mip6‐GFP protein was undetectable by confocal microscopy, probably due to its low abundancy . We therefore expressed Mip6 under the control of the ADH1 promoter ( ADH1 pr) either as a plasmid (p‐ ADH1 pr‐Mip6‐GFP) or at its genomic locus (g‐ ADH1 pr‐Mip6‐GFP), both of which resulted in increased Mip6 expression levels (Fig A).…”

The RNA binding protein Mip6, a novel cellular partner of Mex67 export factor with implications in mRNA export

“…Another study that dealt with both Mip6 and Pes4 also suggested a role for Mip6 in regulating steady state expression, protection, and mRNA localization during stress conditions (Jin et al, 2017). They also found that during stress induced sporulation, Mip6 localizes to cytoplasmic foci that contained mRNA transcripts which Mip6 protected from degradation.…”

“…Although both had a role during cellular stress induced sporulation (Jin et al, 2017), and both re-localize to cytoplasmic foci, however each protein displayed distinct cytoplasmic protein localization. Moreover, while the protection for few mRNA transcripts by either Mip6 or Pes4 during sporulation was redundant, many mRNA transcripts were uniquely protected by either Mip6 or Pes4.…”

“…In the very few literature references on Mip6 or Pes4, the proteins were usually referred to as putative RNA binding proteins containing three RRMs (Bolognesi et al, 2016;Jin, Zhang, Sternglanz, & Neiman, 2017;Segref et al, 1997). In the only two papers on the subject, The "predicted" RRM domains of Mip6 or both Mip6 and Pes4, are said to be critical for their function: formation of cytoplasmic foci containing RNA when Mip6 is over-expressed (Bolognesi et al, 2016), and the role of both Mip6 and Pes4 in mRNA protection and localization in stress conditions (Jin et al, 2017).…”

“…In the only two papers on the subject, The "predicted" RRM domains of Mip6 or both Mip6 and Pes4, are said to be critical for their function: formation of cytoplasmic foci containing RNA when Mip6 is over-expressed (Bolognesi et al, 2016), and the role of both Mip6 and Pes4 in mRNA protection and localization in stress conditions (Jin et al, 2017). However though, no one had actually demonstrated the ability of these proteins to bind RNA in vitro or in vivo or looked closer at the number and diversity of RRMs they contained.…”