Ubiquitin Is Added to Proteins Targeted for Degradation by Formation

Ubiquitin is added to proteins targeted for degradation by formation of a(n) :

A) ester bond between the C-terminus of ubiquitin and a serine of the target protein.
B) thioester bond between the C-terminus of ubiquitin and a cysteine of the target protein.
C) amide bond between the C-terminus of ubiquitin and a lysine of the target protein.
D) ester bond between a glutamate of ubiquitin and a serine in the target protein.
E) thioester bond between a glutamate of ubiquitin and a cysteine in the target protein.