Although the inhibitory mechanism is similar to that used in U1A autoregulation, U1A within the U1 snRNP does not contribute to PAP inhibition. Instead the U1 70K protein, when bound to U1 snRNA, both interacts with and inhibits PAP. Conservation of the U1 70K inhibitory domains suggests that...
(dU1-70K) is a likely candidate to mediate an interaction with PSI because the human U1-70K protein is known to mediate functional interactions, through its C-terminal arginine-serine (RS)-rich domain, with non-snRNP splicing factors of the SR protein family Cao and Garcia-Blanco 1998, ...