Control of Poly(A) Length

Baker, Ellen J.

doi:10.1016/b978-0-08-091652-1.50019-0

Cited by 20 publications

(14 citation statements)

References 178 publications

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“…That is, at low temperatures deadenylation may predispose the mRNA for turnover, a suggestion that has been made previously for other mRNAs (6,25,70). As discussed recently, such a cause-and-effect relationship is difficult to prove by existing methods (9).…”

Section: Discussionmentioning

confidence: 86%

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Preferential deadenylation of Hsp70 mRNA plays a key role in regulating Hsp70 expression in Drosophila melanogaster.

1994

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Following a standard heat shock, -40%o ofHsp7O transcripts in Drosophila melanogaster lack a poly(A) tail. Since heat shock disrupts other aspects of RNA processing, this observation suggested that heat might disrupt polyadenylation as well. We find, however, that as the temperature is increased a larger fraction of Hsp7O RNA is polyadenylated. Poly(A)-deficient Hsp7O RNAs arise not from a failure in polyadenylation but from the rapid and selective removal of poly(A) from previously adenylated transcripts. Poly(A) removal is highly regulated: poly(A) is (i) removed much more rapidly from Hsp7O RNAs than from Hsp23 RNAs, (ii) removed more rapidly after mild heat shocks than after severe heat shocks, and (iii) removed more rapidly after a severe heat shock if cells have first been conditioned by a mild heat treatment. Poly(A) seems to be removed by simple deadenylation rather than by endonucleolytic cleavage 5' of the adenylation site. During recovery from heat shock, deadenylation is rapidly followed by degradation. In cells maintained at high temperatures, however, the two processes are uncoupled and Hsp7O RNAs are deadenylated without being degraded. These deadenylated mRNAs are translated with low efficiency. Deadenylation therefore allows Hsp7O synthesis to be repressed even when degradation of the mRNA is blocked. Poly(A) tail shortening appears to play a key role in regulating Hsp7O expression.The most abundant and tightly regulated heat-inducible protein in Drosophila melanogaster is Hsp7O (47,62). Hsp7O and its relatives make up a highly conserved protein family, with eukaryotic, eubacterial, and archaebacterial members sharing at least 50% amino acid identity (27,30,47). Eukaryotes have several Hsp7O proteins. Some are constitutive and are required for normal growth, whereas others are heat inducible and help organisms cope with the toxic effects of heat. In D. melanogaster the haploid genome encodes five virtually identical heat-inducible Hsp7O proteins (32), which share -70 to 80% amino acid identity with their constitutively expressed relatives (61, 64). Consistent with their independent patterns of regulation, the 3' and 5' sequences of the constitutive genes share little or no homology with those of the heat-inducible genes.The heat- strategies are used. First, the absence of introns in the Hsp7O gene (31) allows its transcripts to circumvent the high-temperature-induced block in mRNA splicing and move rapidly into the cytoplasm (91). Second, high temperatures block the turnover of the normally short-lived Hsp7O mRNA, allowing it to accumulate very rapidly to high concentrations (67). Third, the translation of normal cellular mRNAs is inhibited at high temperatures by mechanisms that act at the levels of both initiation and elongation (8,33,45,80). Hsp7O mRNAs are translated efficiently under these conditions because special sequences in their 5' untranslated leaders allow them to circumvent the block in translation (51; for a review, see reference 46).After return to normal temperatures, hsp synthe...

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Section: Discussionmentioning

confidence: 86%

“…Also, after a severe heat shock, deadenylation occurs more rapidly in cells that have been preconditioned by a mild heat treatment than in cells that have not been preconditioned. There are only a few other known cases in which deadenylation is subject to such dynamic regulation (6,89).…”

Section: Discussionmentioning

confidence: 99%

Preferential deadenylation of Hsp70 mRNA plays a key role in regulating Hsp70 expression in Drosophila melanogaster.

1994

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“…Polyadenylation was inhibited by the addition of 3'-dATP and the mRNA degradation rate was examined. 3'-deoxyadenosine-triphosphate (cordycepin triphosphate, 3'-dATP) is an ATP analog and a known inhibitor of nuclearencoded RNA polyadenylation (Baker, 1993). Chloroplasts were isolated from young spinach leaves, lysed in a minimal volume of buffer (see Experimental procedures), and incubated at room temperature in the absence or presence of ATP (as a control) or 3'-dATE The internal ATP concentration of the degradation system was 0.3 mM as determined by the luciferin-luciferase assay.…”

Section: Resultsmentioning

confidence: 99%

Blocking polyadenylation of mRNA in the chloroplast inhibits its degradation

1997

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SummaryThe addition of poly(A)-rich sequences to endonuclease cleavage products of chloroplast mRNA has recently been suggested to target the polyadenylated RNA for rapid exonucleolytic degradation. This study analyzed whether the addition of a poly(A)-rich tail to RNA molecules is required for degradation by chloroplast exonuclease(s). In lyzed chloroplasts from spinach, addition of the polyadenylation inhibitor, cordycepin triphosphate (3'-dATP), inhibited the degradation of psbA and rbcL mRNAs. Furthermore, degradation intermediates generated by endonucleolytic cleavages accumulated. Similar results were obtained when yeast tRNA was added to the mRNA degradation system as a non-specific exoribonuclease inhibitor. Nevertheless, the stabilization mechanisms differ: while tRNA directly affects the exonuclease activity, 3'dATP has an indirect effect by inhibiting polyadenylation. The results indicate that the addition of poly(A)-rich sequences to endonucleolytic cleavage products of chloroplast mRNA is required to target these RNAs for rapid exonucleolytic degradation. Together with previous work, the data reported here support a model for mRNA degradation in the chloroplast in which endonucleolytic cleavages are followed by the addition of poly(A)-rich sequences to the proximal cleavage products, targeting these RNAs for rapid exonucleolytic decay.

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“…PABP is now considered a multifunctional protein and is proposed to participate in translation initiation, mRNA deadenylation, inhibition of mRNA decapping, and mRNP maturation (4,12,16,20,27,75).…”

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confidence: 99%

Efficient Cleavage of Ribosome-Associated Poly(A)-Binding Protein by Enterovirus 3C Protease

Kuyumcu-Martinez

Joachims

Lloyd

2002

J Virol

124

134

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Poliovirus (PV) causes a rapid and drastic inhibition of host cell cap-dependent protein synthesis during infection while preferentially allowing cap-independent translation of its own genomic RNA via an internal ribosome entry site element. Inhibition of cap-dependent translation is partly mediated by cleavage of an essential translation initiation factor, eIF4GI, during PV infection. In addition to cleavage of eIF4GI, cleavage of eIF4GII and poly(A)-binding protein (PABP) has been recently proposed to contribute to complete host translation shutoff; however, the relative importance of eIF4GII and PABP cleavage has not been determined. At times when cap-dependent translation is first blocked during infection, only 25 to 35% of the total cellular PABP is cleaved; therefore, we hypothesized that the pool of PABP associated with polysomes may be preferentially targeted by viral proteases.

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Control of Poly(A) Length

Cited by 20 publications

References 178 publications

Preferential deadenylation of Hsp70 mRNA plays a key role in regulating Hsp70 expression in Drosophila melanogaster.

Preferential deadenylation of Hsp70 mRNA plays a key role in regulating Hsp70 expression in Drosophila melanogaster.

Blocking polyadenylation of mRNA in the chloroplast inhibits its degradation

Efficient Cleavage of Ribosome-Associated Poly(A)-Binding Protein by Enterovirus 3C Protease

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