7The Yeast mRNA-binding Protein Npl3p Interacts with the Cap-binding Complex

Abstract

A number of RNA-binding proteins are associated with mRNAs in both the nucleus and the cytoplasm. One of these, Npl3p, is a heterogeneous nuclear ribonucleoprotein-like protein with some similarity to SR proteins and is essential for growth in the yeast S. cerevisiae. Temperature-sensitive alleles have defects in the export of mRNA out of the nucleus (1). In this report, we define a genetic relationship between NPL3 and the nonessential genes encoding the subunits of the cap-binding complex (CBP80 and CBP20). Deletion of CBP80 or CBP20 in combination with certain temperature-sensitive npl3 mutant alleles fail to grow and thus display a synthetic lethal relationship. Further evidence of an interaction between Npl3p and the cap-binding complex was revealed by co-immunoprecipitation experiments; Cbp80p and Cbp20p specifically co-precipitate with Npl3p. However, the interaction of Npl3p with Cbp80p depends on both the presence of Cbp20p and RNA. In addition, we show that Cbp80p is capable of shuttling between the nucleus and the cytoplasm in a manner dependent on the ongoing synthesis of RNA. Taken together, these data support a model whereby mRNAs are co-transcriptionally packaged by proteins including Npl3p and capbinding complex for export out of the nucleus.While in the nucleus, mRNA precursors, referred to as pre-mRNAs or heterogeneous nuclear RNAs undergo a series of processing events before entering the cytoplasm. These maturation events include co-transcriptional capping at the 5Ј-end, splicing, and cleavage and polyadenylation at the 3Ј-end. The proper execution of these steps affects the export of mRNA (reviewed in Refs. 2-4). Thus, the process of mRNA export commences long before the RNA actually reaches the nuclear membrane.

Quality control of spliced mRNAs requires the shuttling SR proteins Gbp2 and Hrb1

“…In fact, genetic and physical interactions have been described with the cap binding complex (CBC) components Cbp20 and Cbp80 (ref. 33). …”

The C-terminal domain of myosin-like protein 1 (Mlp1p) is a docking site for heterogeneous nuclear ribonucleoproteins that are required for mRNA export

“…Cells were lysed and myc-tagged proteins were immunoprecipitated from protein extracts (8 mg total protein) with agarose-conjugated myc Ab (9E-10, Santa Cruz Biotechnology) (26). For RNase-treated samples, protein lysates were treated with 15 units (200 g) RNase A for 30 min at 4°C (30). For immunoprecipitation of protein A-tagged Mlp1p, Mlp1p-protein A (ACY683) and WT (ACY192) cells were grown to log phase and collected by centrifugation.…”

Nuclear export of mRNA and its regulation by ubiquitylation

“…In fact, a major progress has been made in last several years towards understanding the nuclear export of mRNA and its coupling to transcription, mRNA processing and post-translational modifications. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] Here, we highlight the recent advances of mRNA export with disease pathogenesis.…”

“…[7][8][9][15][16][17][18][19][20][21][22][23][24][25] Thus, improperly processed mRNAs are not exported. Further, such a coupling of mRNA export with processing events provides a quality control to export properly processed mRNA for translation.…”