Attaching a single unit of this protein to P.C.N.A induces translesion synthesis, while adding further copies of this protein in a chain promotes the template-switching pathway. Loss of E.6-A.P, which attaches this protein, causes Angelman syndrome. Like many enzymes that recognise this protein, the V.H.L protein contains a RING finger domain. During (15[1])S-phase, cyclins D and E are modified with this protein by the S.C.F complex. Chains of this protein are most commonly (*) K48- or K63-linked. Attaching this protein to a substrate via one of its 7 lysine residues involves a cascade of activation, conjugation, and ligation steps catalysed by namesake E1, E2 and (10[1])E3 enzymes. Unlike the related SUMO proteins, this protein is used to tag proteins destined for proteasomal degradation. For 10 points, which small protein is named for its presence in nearly (10[1])all cells? ■END■