Phosphorylation can modify protein function, localization, and conformation by interfering with protein-protein interactions. It has been reported that in ataxin1, phosphorylation at serine 776 is dependent upon the length of the polyQ tract. Replacing this residue with an alanine thus preventing its phosphorylation considerably reduced cerebellar neuropathology in SCA1: polyQ ataxin-1 in which serine 776 is mutated to alanine displayed substantially reduced Purkinje cell degeneration. In another example, taking into account that expanded polyglutamine androgen receptor (AR) is phosphorylated by Akt, it has been demonstrated that substitution of the AR at two Akt consensus sites, serine 215 and serine 792 in SBMA models, with aspartate, which mimics phosphorylation, blocked ligand binding and lessened toxicity. Acetylation, the binding of an acetyl group with lysine residues in a protein, is a modification known to modulate protein-protein and protein-DNA interactions and control, typically increasing, protein stability. In SCA7, acetylation at lysine 257 elevates protein stability, and is suggested important for disease toxicity. In SBMA, acetylation at lysine 632/633 controls nuclear entry as well as the folding of androgen receptor protein. Small ubiquitin-like modifier (SUMO) proteins are known to bind to specific lysine residues in target proteins modifying their cellular localization, protein-protein interactions, and transcription factors activation. SUMOylation refers to the SUMO moiety being attached to a lysine residue in the target protein. SUMO has been detected to colocalize with neuronal inclusion bodies in the brains of patients and cell models with HD, SCA3, and DRPLA thus suggesting that SUMO modification contributes to neurodegeneration in polyQ disease. Furthermore, certain post-translational modifications can be mutually linked to one another. For example, phosphorylation impacts the proteolytic cleavage of polyQ proteins; it can also affect SUMOylation and ubiquitylation. SUMOylation and ubiquitylation can compete for the same lysine residues, as suggested for htt, etc. (Figure ).