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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. 相似文献
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An exclusively nuclear RNA-binding protein affects asymmetric localization of ASH1 mRNA and Ash1p in yeast 总被引:1,自引:0,他引:1
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Long RM Gu W Meng X Gonsalvez G Singer RH Chartrand P 《The Journal of cell biology》2001,153(2):307-318
The localization of ASH1 mRNA to the distal tip of budding yeast cells is essential for the proper regulation of mating type switching in Saccharomyces cerevisiae. A localization element that is predominantly in the 3'-untranslated region (UTR) can direct this mRNA to the bud. Using this element in the three-hybrid in vivo RNA-binding assay, we identified a protein, Loc1p, that binds in vitro directly to the wild-type ASH1 3'-UTR RNA, but not to a mutant RNA incapable of localizing to the bud nor to several other mRNAs. LOC1 codes for a novel protein that recognizes double-stranded RNA structures and is required for efficient localization of ASH1 mRNA. Accordingly, Ash1p gets symmetrically distributed between daughter and mother cells in a loc1 strain. Surprisingly, Loc1p was found to be strictly nuclear, unlike other known RNA-binding proteins involved in mRNA localization which shuttle between the nucleus and the cytoplasm. We propose that efficient cytoplasmic ASH1 mRNA localization requires a previous interaction with specific nuclear factors. 相似文献
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Gonsalvez GB Urbinati CR Long RM 《Biology of the cell / under the auspices of the European Cell Biology Organization》2005,97(1):75-86
RNA localization is a widely utilized strategy employed by cells to spatially restrict protein function. In Saccharomyces cerevisiae asymmetric sorting of mRNA to the bud has been reported for at least 24 mRNAs. The mechanism by which the mRNAs are trafficked to the bud, illustrated by ASH1 mRNA, involves recognition of cis-acting localization elements present in the mRNA by the RNA-binding protein, She2p. The She2p/mRNA complex subsequently associates with the myosin motor protein, Myo4p, through an adapter, She3p. This ribonucleoprotein complex is transported to the distal tip of the bud along polarized actin cables. While the mechanism by which ASH1 mRNA is anchored at the bud tip is unknown, current data point to a role for translation in this process, and the rate of translation of Ash1p during the transport phase is regulated by the cis-acting localization elements. Subcellular sorting of mRNA in yeast is not limited to the bud; certain mRNAs corresponding to nuclear-encoded mitochondrial proteins are specifically sorted to the proximity of mitochondria. Analogous to ASH1 mRNA localization, mitochondrial sorting requires cis-acting elements present in the mRNA, though trans-acting factors involved with this process remain to be identified. This review aims to discuss mechanistic details of mRNA localization in S. cerevisiae. 相似文献
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Structural elements required for the localization of ASH1 mRNA and of a green fluorescent protein reporter particle in vivo 总被引:1,自引:0,他引:1
The sorting of the Ash1 protein to the daughter nucleus of Saccharomyces cerevisiae in late anaphase of the budding cycle correlates with the localization of ASH1 mRNA at the bud tip [1] [2]. Although the 3' untranslated region (3' UTR) of ASH1 is sufficient to localize a reporter mRNA, it is not necessary, a result which indicates that other sequences are involved [1]. We report the identification of three additional cis-acting elements in the coding region. Each element alone, when fused to a lacZ reporter gene, was sufficient for the localization of the lacZ mRNA reporter to the bud. A fine-structure analysis of the 3' UTR element showed that its function in mRNA localization did not depend on a specific sequence but on the secondary and tertiary structure of a minimal 118 nucleotide stem-loop. Mutations in the stem-loop that affect the localization of the lacZ mRNA reporter also affected the formation of the localization particles, in living cells, composed of a green fluorescent protein (GFP) complexed with lacZ-ASH1-3' UTR mRNA [3]. A specific stem-loop in the 3' UTR of the ASH1 mRNA is therefore required for both localization and particle formation, suggesting that complex formation is part of the localization mechanism. An analysis on one of the coding-region elements revealed a comparable stem-loop structure with similar functional requirements. 相似文献
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ASH1 mRNA localization in yeast involves multiple secondary structural elements and Ash1 protein translation 总被引:2,自引:0,他引:2
Localization of ASH1 mRNA to the distal cortex of daughter but not mother cells at the end of anaphase is responsible for the two cells' differential mating-type switching during the subsequent cell cycle. This localization depends on actin filaments and a type V myosin (She1/Myo4). The 3' untranslated region (3' UTR) of ASH1 mRNA is reportedly capable of directing heterologous RNAs to a mother cell's bud [1] [2]. Surprisingly, however, its replacement has little or no effect on the localisation of ASH1 mRNA. We show here that, unlike all other known localization sequences that have been found in 3' UTRs, all the elements involved in ASH1 mRNA localization are located at least partly within its coding region. A 77 nucleotide region stretching from 7 nucleotides 5' to 67 nucleotides 3' of the stop codon of ASH1 mRNA is sufficient to localize mRNAs to buds; the secondary structure of this region, in particular two stems, is important for its localizing activity. Two regions entirely within coding sequences, both sufficient to localize green fluorescent protein (GFP) mRNA to growing buds, are necessary for ASH1 mRNA localization during anaphase. These three regions can anchor GFP mRNA to the distal cortex of daughter cells only inefficiently. The tight anchoring of ASH1 mRNA to the cortex of the daughter cell depends on translation of the carboxy-terminal sequences of Ash1 protein. 相似文献
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RNA-protein interactions promote asymmetric sorting of the ASH1 mRNA ribonucleoprotein complex 总被引:3,自引:0,他引:3
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Gonsalvez GB Lehmann KA Ho DK Stanitsa ES Williamson JR Long RM 《RNA (New York, N.Y.)》2003,9(11):1383-1399
In Saccharomyces cerevisiae, ASH1 mRNA is localized to the tip of daughter cells during anaphase of the cell cycle. ASH1 mRNA localization is dependent on four cis-acting localization elements as well as Myo4p, She2p, and She3p. Myo4p, She2p, and She3p are hypothesized to form a heterotrimeric protein complex that directly transports ASH1 mRNA to daughter cells. She2p is an RNA-binding protein that directly interacts with ASH1 cis-acting localization elements and associates with She3p. Here we report the identification of seven She2p mutants-N36S, R43A, R44A, R52A, R52K, R63A, and R63K-that result in the delocalization of ASH1 mRNA. These mutants are defective for RNA-binding activity but retain the ability to interact with She3p, indicating that a functional She2p RNA-binding domain is not a prerequisite for association with She3p. Furthermore, the nuclear/cytoplasmic distribution for the N36S and R63K She2p mutants is not altered, indicating that nuclear/cytoplasmic trafficking of She2p is independent of RNA-binding activity. Using the N36S and R63K She2p mutants, we observed that in the absence of She2p RNA-binding activity, neither Myo4p nor She3p is asymmetrically sorted to daughter cells. However, in the absence of She2p, Myo4p and She3p can be asymmetrically segregated to daughter cells by artificially tethering mRNA to She3p, implying that the transport and/or anchoring of the Myo4p/She3p complex is dependent on the presence of associated mRNA. 相似文献
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Localization of messenger RNAs and local protein synthesis contribute to asymmetric protein distribution not only of cytoplasmic but also of membrane or secreted proteins. Since synthesis of the latter protein classes occurs at the rough endoplasmic reticulum (ER), mRNA localization and distribution of ER should be coordinated. However, this coordination is not yet understood. In yeast, mRNA localization to the growing bud depends on the myosin Myo4p, its adaptor She3p, and the specific RNA binding protein She2p. These proteins mediate the localization of 23 mRNAs including ASH1 mRNA and mRNAs encoding membrane proteins. In addition, Myo4p and She3p are required for segregation of cortical ER to the bud. Here we show, with ASH1 mRNA as a model mRNA, that localizing messenger ribonucleoprotein (mRNP) particles comigrate with tubular ER structures to the bud, which requires the RNA binding protein She2p. Coordinated movement of the ASH1 mRNP with ER tubules but not their association with each other depends on Myo4p and She3p. Subcellular fractionation experiments demonstrate a cosegregation of ER and She2p, which is independent of Myo4p, She3p, or polysomes. Our findings suggest a novel model for mRNA localization that involves association of She2p and mRNPs with ER tubules and myosin-dependent cotransport of tubules and localized mRNPs. 相似文献
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Localization and anchoring of mRNA in budding yeast. 总被引:19,自引:0,他引:19
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mRNA trafficking in fungi 总被引:1,自引:0,他引:1
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