An extended PAXT connection is required for turnover of nuclear polyadenylated RNA in human cells

Recruitment of the human ribonucleolytic RNA exosome to nuclear polyadenylated (pA+) RNA is facilitated by the Poly(A) Tail eXosome Targeting (PAXT) connection. Besides its core dimer, formed by the exosome co-factor MTR4 and the ZFC3H1 protein, the PAXT connection remains poorly defined. By characterizing nuclear pA+-RNA bound proteomes as well as MTR4-ZFC3H1 containing complexes in conditions favoring PAXT assembly, we here uncover
three additional proteins required for PAXT function: ZC3H3, RBM26/RBM27 and the known PAXT-associated protein, PABPN1. The zinc-finger protein ZC3H3 interacts directly with MTR4-ZFC3H1 and loss of either identified PAXT
component results in the accumulation of PAXT substrates. Collectively, our results establish new factors involved in the turnover of nuclear pA+ RNA and suggest that these are limiting for PAXT activity.