Asc1p, a WD40-domain containing adaptor protein, is required for the interaction of the RNA-binding protein Scp160p with polysomes

Abstract

Scp160p interacts in an mRNA-dependent manner with translating ribosomes via multiple RNA-binding heterogeneous nuclear ribonucleoprotein K-homology (KH) domains. In the present study, we show by protein-protein cross-linking that Scp160p is in close proximity to translation elongation factor 1A and the WD40 (Trp-Asp 40)-repeat containing protein Asc1p at ribosomes. Analysis of a truncation mutant revealed that the C-terminus of Scp160p is essential for ribosome binding and that Cys(1067) at the C-terminus of Scp160p is required to obtain these cross-links. The interaction of Scp160p with ribosomes depends on Asc1p. In fast-growing yeast cells, nearly all Asc1p is tightly bound to ribosomes, but it can also be present in a ribosome-free form depending on growth conditions. The functional homologue of Asc1p, mammalian RACK1 (receptor of activated C kinase), was previously characterized as an adaptor protein bridging activated signalling molecules with their substrates. Our results suggest that Scp160p connects specific mRNAs, ribosomes and a translation factor with an adaptor for signalling molecules. These interactions might regulate the translation activity of ribosomes programmed with specific mRNAs.

The SESA network links duplication of the yeast centrosome with the protein translation machinery

“…In response to SPB duplication defects, the SESA network, comprising of the known mRNA-binding protein Scp160 (Frey et al 2001;Li et al 2003Li et al , 2004Baum et al 2004), the ribosomeassociated Asc1 (Baum et al 2004;Gerbasi et al 2004), the translation inhibitor Eap1 (Cosentino et al 2000), and the protein Smy2 (Kofler et al 2005), was identified as being responsible for the translation control of POM34 mRNA. We demonstrate that SESA inhibits translation of POM34 mRNA by binding of the 4E-BP Eap1 to the conserved translation initiation factor eIF4E.…”

“…S7). Scp160 shows genetic and biochemical interactions with the Asc1 protein, which is a core component of the 40S ribosomal subunit and as such binds Scp160 to ribosomes (Baum et al 2004;Nilsson et al 2004). However, also a cytoplasmic pool of Asc1 exists (Brodersen and Nissen 2005) that may direct the SESA-POM34 mRNA complex to ribosomes.…”

“…We analyzed about 40 genes with roles in translation control, the UPR pathway (Sidrauski and Walter 1997), and nuclear envelope function (Supplemental Table 1) for their requirement in the viability of mps2D 2mm-SMY2 cells. This analysis identified the genes coding for the polysomeassociated, mRNA-binding protein Scp160 that has been shown to exist in a complex with Eap1 (Mendelsohn et al 2003), the Scp160-interacting protein Asc1 (essential for ER localization of Scp160) (Baum et al 2004), and the brefeldin A resistance protein Bfr1 (a component of polyribosome-associated mRNP complexes) (Lang et al 2001), as being essential in the mps2D 2mm-SMY2 background (Figs. 2E,F, 3A; Supplemental Table 1).…”

“…The mRNA-binding protein Scp160 could target mRNAs to SESA regulation (Frey et al 2001;Baum et al 2004;Li et al 2004). A microarray analyses of mRNAs released from affinity isolated Scp160-containing complexes identified a limited set of mRNAs that bind to Scp160 .…”

Is Ribosome Synthesis Controlled by Pol I Transcription?

“…(2) Group B (see Table 1) includes eight genes whose products are involved in ribosome synthesis, assembly and/or function: Utp22 is involved in the 35S primary transcript processing, 18 Emg1 is required for the maturation of the 18S rRNA and for 40S ribosome production, 19 Stm1 directly binds to mature 80S ribosomes and polysomes, 20 Rpg1 is a translation initiation factor, 21 Asc1 acts as a negative regulator of translation, 22 and Cdc60 aminoacylates leucyl-tRNA. 23 Finally, SDC1 and SPP1, whose products are two subunits of the COMPASS (Set1C) complex which methylates lysine 4 of histone H3, and which is involved in rDNA silencing, 24,25 are also specifically deregulated in CARA cells during the rapamycin treatment.…”