Intra-Nuclear Function for PP2A Phosphatase: Pph21/22 Are Required for Rapamycin-Induced GATA Factor Binding to the DAL5 Promoter in Yeast.

PP2A, a central Tor pathway phosphatase consisting of a catalytic subunit (Pph21 or Pph22), a scaffold subunit (Tpd3) and one of two regulatory subunits (Cdc55 or Rts1) has been repeatedly shown to play important roles in cytoplasmically-localized signal transduction activities. In contrast, its involvement in intra-nuclear control of messenger RNA ...
production has heretofore not been reported. Here, we demonstrate for the first time that binding of the Nitrogen Catabolite Repression-responsive GATA transcription activators (Gln3 & Gat1) to the DAL5 promoter and DAL5 expression require Pph21/22-Tpd3-Cdc55/Rts1 in rapamycin-treated glutamine-grown cells. This conclusion is supported by the following observations: (i) Rapamycin-induced DAL5 expression along with Gln3 and Gat1 binding to the DAL5 promoter fail to occur in pph21Δpph22Δ, tpd3Δ, and cdc55Δrts1Δ mutants. (ii) The Pph21/22 requirement persists even when Gat1 and Gln3 are rendered constitutively nuclear thus dissociating the intra-nuclear requirement of PP2A from its partial requirement for rapamycin-induced nuclear Gat1 localization. (iii) Pph21-Myc(13) weakly associates with the DAL5 promoter in a Gat1-dependent manner, whereas similar Pph22-Myc(13) association requires both Gln3 and Gat1. Finally, we demonstrate that a pph21Δpph22Δ is epistatic to ure2Δ for nuclear Gat1 localization in untreated glutamine-grown cells, whereas for Gln3 just the opposite occurs, i.e., the ure2Δ is epistatic to a pph21Δpph22Δ. This final observation adds additional support to our previous conclusion that the Gln3 and Gat1 GATA factor localizations are predominantly controlled by different regulatory pathways.
Date: Oct. 25, 2010
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