Recognition of SUMO-modified PCNA requires tandem receptor motifs in Srs2

Abstract

Ubiquitin (Ub) and ubiquitin-like (Ubl) modifiers such as SUMO mediate signal transduction through post-translational modification of substrate proteins in pathways that control differentiation, apoptosis, the cell cycle, and responses to stress such as the DNA damage response. In yeast, the proliferating cell nuclear antigen PCNA is modified by ubiquitin in response to DNA damage and by SUMO during S-phase. While Ub-PCNA can signal for recruitment of translesion DNA polymerases, SUMO-PCNA signals for recruitment of the anti-recombinogenic DNA helicase Srs2. It remains unclear how receptors such as Srs2 specifically recognize substrates after conjugation to Ub/Ubls. Here we show through structural, biochemical and functional studies that the Srs2 C-terminal domain harbors tandem receptor motifs that interact independently with PCNA and SUMO and that both motifs are required to specifically recognize SUMO-PCNA. The mechanism presented herein is pertinent to understanding how other receptors specifically recognize Ub/Ubl-modified substrates to facilitate signal transduction.

The Ubiquitin–Proteasome System of Saccharomyces cerevisiae

“…This SUMOylation event prevents unscheduled recombination by recruiting an antirecombinogenic helicase, Srs2 (Papouli et al 2005;Pfander et al 2005). As with the recruitment of damagetolerant polymerases by monoubiquitylated PCNA, Srs2 is targeted to SUMO-modified PCNA by means of tandem receptor motifs that independently recognize SUMO and PCNA (Armstrong et al 2012). Under conditions of replication stress, Srs2 thus allows damage processing by ubiquitin-dependent bypass.…”

Poly-Small Ubiquitin-like Modifier (PolySUMO)-binding Proteins Identified through a String Search

“…The SBDs in Arkadia and FLASH may be particularly fitted for this kind of SUMO binding, where the SIMs are further separated and presumably more flexible. The avidity effect due to multiple SIM-SUMO contacts may thus provide sufficient affinity and specificity for the formation of sumoylation-regulated protein complexes, which would be distinct from those involving a singular SIM and often a secondary, SUMO-independent physical contact (44,45). Furthermore, it is also conceivable that clustered SIMs form a folded ␤-sheet (Fig.…”

Local regulation of the Srs2 helicase by the SUMO-like domain protein Esc2 promotes recombination at sites of stalled replication

“…Srs2 belongs to the UvrD family of DNA helicases and interacts preferentially with SUMOylated PCNA by means of two adjacent interaction motifs for PCNA and SUMO present at its C terminus (Papouli et al 2005;Pfander et al 2005;Armstrong et al 2012;Kolesar et al 2012). Biochemically, Srs2 eliminates recombination intermediates by disrupting or preventing the formation of Rad51 presynaptic filaments (Krejci et al 2003;Veaute et al 2003;Robert et al 2006).…”