Overexpression results in additional interactions of excess HMR beyond the HMR core complex.

(A) Differential interaction proteome between endogenously FLAG tagged HMR (HMR^endo_, n = 4) and ectopically expressed HMR (HMR^wt-tg, n = 9). Only proteins enriched in HMR^wt-tg or HMR^endo vs CTRL (p < 0.05) were considered. Components of the HMR core complex and HP1a are shown in red, all other factors in blue. To display the differences within the HMR^endo and HMR^wt-tg interactomes, the enrichment of each putative interactor (Log2(iBAQ^HMR*/IBAQ^control)) was normalized to the enrichment of the HMR protein used as bait. The resulting values were then plotted against each other. Dots below the diagonal indicate a stronger enrichment in the HMR^endo pull down, the dots above the diagonal a stronger enrichment in the ectopically expressed HMR. (B) Differences of the ratio between HMR and members of the HMR complex and HP1a with and without ectopic expression of HMR. Plotted is the relative enrichment of each HMR complex member to the enrichment of the HMR used as bait (= the offset from the diagonal). Error bars reflect the standard error of the means (SEM). (C) Network diagram of all factors enriched in the AP-MS experiments of HMR^endo or HMR^wt-tg (p < 0.05). Red nodes represent HMR complex components and HP1a, blue nodes additional HMR binders. Nodes containing Zn-finger domains have a diamond shape. Solid edges connect the HMR complex and HP1a, dotted edges reflect protein-protein interactions predicted using the string database [22], dashed edges reflect protein-protein interaction identified by AP-MS experiments performed in this work (Fig 1 and S3 Table). In (A) and (B) proteins were labelled only if enriched in HMR^wt-tg or HMR^endo vs CTRL (p < 0.05).