Polarized growth in the budding yeast Saccharomyces cerevisiae depends upon the asymmetric localization and enrichment of polarity and secretion factors at the membrane prior to budding. We examined how these factors (i.e., Cdc42, Sec4, and Sro7) reach the bud site and found that their respective mRNAs localize to the tip of the incipient bud prior to nuclear division. Asymmetric mRNA localization depends upon factors that facilitate ASH1 mRNA localization (e.g., the 3 untranslated region, She proteins 1 to 5, Puf6, actin cytoskeleton, and a physical association with She2). mRNA placement precedes protein enrichment and subsequent bud emergence, implying that mRNA localization contributes to polarization. Correspondingly, mRNAs encoding proteins which are not asymmetrically distributed (i.e., Snc1, Mso1, Tub1, Pex3, and Oxa1) are not polarized. Finally, mutations which affect cortical endoplasmic reticulum (ER) entry and anchoring in the bud (myo4⌬, sec3⌬, and srp101) also affect asymmetric mRNA localization. Bud-localized mRNAs, including ASH1, were found to cofractionate with ER microsomes in a She2-and Sec3-dependent manner; thus, asymmetric mRNA transport and cortical ER inheritance are connected processes in yeast.

mRNA localization may be an important determinant for protein localization. We describe a simple PCR-based genomic-tagging strategy (m-TAG) that uses homologous recombination to insert binding sites for the RNA-binding MS2 coat protein (MS2-CP) between the coding region and 3' untranslated region (UTR) of any yeast gene. Upon coexpression of MS2-CP fused with GFP, we demonstrate the localization of endogenous mRNAs (ASH1, SRO7, PEX3 and OXA1) in living yeast (Saccharomyces cerevisiae).

The mechanism of RNA degradation in Escherichia coli involves endonucleolytic cleavage, polyadenylation of the cleavage product by poly(A) polymerase, and exonucleolytic degradation by the exoribonucleases, polynucleotide phosphorylase (PNPase) and RNase II. The poly(A) tails are homogenous, containing only adenosines in most of the growth conditions. In the chloroplast, however, the same enzyme, PNPase, polyadenylates and degrades the RNA molecule; there is no equivalent for the E. coli poly(A) polymerase enzyme. Because cyanobacteria is a prokaryote believed to be related to the evolutionary ancestor of the chloroplast, we asked whether the molecular mechanism of RNA polyadenylation in the Synechocystis PCC6803 cyanobacteria is similar to that in E. coli or the chloroplast. We found that RNA polyadenylation in Synechocystis is similar to that in the chloroplast but different from E. coli. No poly(A) polymerase enzyme exists, and polyadenylation is performed by PNPase, resulting in heterogeneous poly(A)-rich tails. These heterogeneous tails were found in the amino acid coding region, the 5 and 3 untranslated regions of mRNAs, as well as in rRNA and the single intron located at the tRNA fmet . Furthermore, unlike E. coli, the inactivation of PNPase or RNase II genes caused lethality. Together, our results show that the RNA polyadenylation and degradation mechanisms in cyanobacteria and chloroplast are very similar to each other but different from E. coli.The molecular mechanism of RNA degradation in prokaryotes and organelles includes a series of sequential steps. The degradation starts with the initial endonucleolytic cleavage carried out primarily by the endoribonuclease E (RNase E). The cleavage products are then polyadenylated at their 3Ј ends by the poly(A) polymerase (PAP) 1 enzyme in Escherichia coli and the polynucleotide phosphorylase (PNPase) in the chloroplast. The polyadenylated molecules are then rapidly degraded exonucleolytically by PNPase and ribonuclease II (RNase II) (1-3). Finally, the remaining short oligoribonucleotides are degraded by the oligoribonuclease enzyme (4). Although the inhibition of polyadenylation in the chloroplast inhibited exonucleolytic degradation, implying that this is the only mechanism in the RNA degradation process, two RNA degradation mechanisms, a polyadenylation-dependent and a polyadenylation-independent one, were suggested to take place in E. coli (5, 6). Polyadenylation in E. coli is carried out primarily by PAP (7). Also in this bacterium, the RNase E enzyme, part of the PNPase population, an RNA helicase, some RNA molecules, and the glycolytic enzyme enolase are associated in a high molecular weight complex called a degradosome (8).In the chloroplast, the photosynthetic organelle of the plant cell is believed to have an evolutionary prokaryotic origin; many characteristics of the gene expression system resemble those of bacteria. When the RNA degradation mechanism was analyzed in the chloroplast, it was found to be very similar to that of E. coli (1-3). However...

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SummaryIn contrast to detailed knowledge regarding the biosynthesis of anthocyanins, the largest group of plant pigments, little is known about their in planta degradation. It has been suggested that anthocyanin degradation is enzymatically controlled and induced when beneficial to the plant. Here we investigated the enzymatic process in Brunfelsia calycina flowers, as they changed color from purple to white.We characterized the enzymatic process by which B. calycina protein extracts degrade anthocyanins. A candidate peroxidase was partially purified and characterized and its intracellular localization was determined. The transcript sequence of this peroxidase was fully identified.A basic peroxidase, BcPrx01, is responsible for the in planta degradation of anthocyanins in B. calycina flowers. BcPrx01 has the ability to degrade complex anthocyanins, it co-localizes with these pigments in the vacuoles of petals, and both the mRNA and protein levels of BcPrx01 are greatly induced parallel to the degradation of anthocyanins. Both isoelectric focusing (IEF) gel analysis and 3D structure prediction indicated that BcPrx01 is cationic.Identification of BcPrx01 is a significant breakthrough both in the understanding of anthocyanin catabolism in plants and in the field of peroxidases, where such a consistent relationship between expression levels, in planta subcellular localization and activity has seldom been demonstrated.