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J. Biol. Chem., Vol. 279, Issue 6, 4027-4033, February 6, 2004

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Pentobarbital-mediated Regulation of Alternative Polyadenylation in Drosophila Glutathione S-Transferase D21 mRNAs^*

Bünyamin Akgül and Chen-Pei D. Tu

From the Department of Biochemistry and Molecular Biology, Intercollege Graduate Program in Genetics, The Pennsylvania State University, University Park, Pennsylvania 16802

Two nearly identical, gstD21(L) and gstD21(S) mRNAs, whose polyadenylation sites differ by 19 nucleotides, are transcribed from the intronless glutathione S-transferase D21 gene in Drosophila. Both mRNAs are intrinsically very labile, but exposure to pentobarbital renders them stabilized beyond what can be attributed to transcriptional activation. We have reconstituted this PB-mediated mRNA stabilization in a transgene (D21L) that contains the full-length gstD21(L) sequence. We have also constructed a similar transgene (D21L-UTR), which matches D21L but excluded the native 3'-UTR. D21L-UTR produces a relatively stable RNA, whose stability is unaffected by pentobarbital. Following pentobarbital treatment of wild-type flies, the levels of gstD21(L) and gstD21(S) mRNAs hold at a relatively constant ratio (L/S) of 1.4 ± 0.2. In transgenic flies, heat shock induction of D21L mRNA changed the L/S ratio to 0.6 ± 0.1, and it was further reduced to 0.3 ± 0.1 as D21L mRNA accumulated in the presence of PB. The ratio returned nearly normal (1.1 ± 0.1) as the D21L mRNA decayed over 12 h after terminating induction. In constrast, when D21L-UTR was present, the ratio remained constant (1.7 ± 0.2) even under various induction conditions and during recovery. Thus, the 3'-UTR, which was the critical difference between these two transgenes, must have some role in determining the L/S ratio. Induced D21L mRNA alone is not sufficient to cause reversible changes in the ratio. Such changes require the presence of pentobarbital. Therefore, pentobarbital may regulate this L/S ratio by affecting the choice of polyadenylation sites for the gstD21 mRNAs through sensing the concentrations of the native 3'-UTR sequences.

Received for publication, September 12, 2003 , and in revised form, November 10, 2003.

^* This work was supported by a grant from the National Institute of Environmental Health Sciences (ES 02678). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Supported by a fellowship from the Turkish Ministry of Education. Present address: Dept. of Biology, Izmir Institute of Technology, Izmir, Turkey.

To whom correspondence should be addressed: 106 Paul M. Althouse Lab, Dept. of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802-4500. Tel.: 814-863-2096; Fax: 814-863-2096/814-863-7024; E-mail: unh{at}psu.edu.

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