E3 ubiquitin-protein ligase that mediates ubiquitination and subsequent proteasomal degradation of target proteins. Functions in the N-end rule pathway of protein degradation, where it specifically recognizes and ubiquitinates proteins with a N-terminal bulky aromatic amino acid (Phe). Does not act on aliphatic hydrophobic and basic N-terminal residues (Arg or Leu) containing proteins. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Truncated N-terminus.