RNA asymmetric distribution and daughter/mother differentiation in yeast - PubMed (original) (raw)

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RNA asymmetric distribution and daughter/mother differentiation in yeast

Xavier Darzacq et al. Curr Opin Microbiol. 2003 Dec.

Abstract

Active transport and localized translation of the ASH1 mRNA at the bud tip of the budding yeast Saccharomyces cerevisiae is an essential process that is required for the regulation of the mating type switching. ASH1 mRNA localization has been extensively studied over the past few years and the core components of the translocation machinery have been identified. It is composed of four localization elements (zipcodes), within the ASH1 mRNA, and at least three proteins, She1p/Myo4p, She2p and She3p. Whereas the movement of the RNA can be attributed to direct interaction with myosin, the regulation of the RNA expression is less well understood. Recent insights have revealed a role for translation that might have a key function in the regulation of Ash1 protein sorting.

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Figures

Figure 1

Figure 1

Mating type switching in the yeast S. cerevisiae. The mating type of a cell is defined by the expression of ‘a’- or ‘α’- specific gene(s) from the active MAT locus. These specific factors are encoded by the transcriptionally silenced HMLa and HMRα loci. Switching to the opposite mating type occurs by gene conversion at the active MAT locus. The template used for this conversion is issued from the silenced HMLa or HMRα locus of the opposite type. HO endonuclease cuts the active MAT locus, initiating this replacement. In daughter cells, the transcriptional repressor Ash1p inhibits the expression of HO, thereby repressing mating type switching (see text for details).

Figure 2

Figure 2

Ash1 mRNA localization. (a) Cartoon of the Ash1 mRNA core locasome transported on an actin filament. E1, E2a, E2b and E3 zipcodes are recognized by the She1–3p complex, providing the motor activity. **(b)**Schematic view of the different steps of ASH1 mRNA bud tip localization (see also Table1). 1 – Nuclear events: ASH1 transcription in late anaphase, association of ASH1 mRNA with She2p, interaction with Loc1p. 2 – Early cytoplasmic events: Assembly of the locasome by association of the newly exported ASH1_mRNA-She2p RNP with She3p and She1p/Myo4p, recruitment to the actin network and interaction with Khd1p and She4p. 3 – Transport of the locasome to the bud tip. She1p/Myo4 provides the motor activity. Role of She4p as a translocation co-factor. 4 – Anchoring and translation at the bud tip: the mechanism of anchoring is still not understood; nevertheless it involves Khd1p and the nascent Ash1p polypeptide. Puf5p and Scp160p are not represented because their role remains largely unknown. (c) Upper image: phase image of a yeast budding cell in early anaphase. Middle image: fluorescent in situ hybridization (FISH) of_ASH1 mRNA using 6 CY3-labeled probes in red and DAPI staining in blue. Lower image: overlay of the two previous images.

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