SJFα is a 13-atom linker PROTAC. SJFα degrades p38α with a DC50 of 7.16 nM, but is far less effective at degrading p38δ (DC50=299 nM) and does not degrade the other p38 isoforms (β and γ) at concentrations up to 2.5 µM[1].
[1]. Smith BE, et al. Differential PROTAC substrate specificity dictated by orientation of recruited E3 ligase. Nat Commun. 2019 Jan 10;10(1):131.