Enzymes that add ubiquitin to proteins have been found in the nucleus of eukaryotic cells. these enzymes would be most likely to regulate gene expression by

a. causing a change in which introns are removed and changing the mature mrna
b. causing degradation of transcription factors and changing which genes are expressed
c. causing degradation of histones and changing chromatin structure
d. causing activation of enhancer-binding proteins

causing degradation of transcription factors and changing which genes are expressed

Explanation:

Ubiquitination  (addition of ubiquitin to a protein) is the first step in protein degradation process, and it directs  protein to the proteasome for degradation. This process involves three steps with specific groups of enzymes to perform them, which are activation with ubiquitin-activating enzymes, conjugation with ubiquitin-conjugating enzymes and ligation with ubiquitin ligases. These enzymes would be most likely to regulate gene expression by causing degradation of transcription factors and changing which genes are expressed.

option number one would be youre best option