CBC–ARS2 stimulates 3′-end maturation of multiple RNA families and favors cap-proximal processing

Abstract

The nuclear cap-binding complex (CBC) stimulates multiple steps in several RNA maturation pathways, but how it functions in humans is incompletely understood. For small, capped RNAs such as pre-snRNAs, the CBC recruits PHAX. Here, we identify the CBCAP complex, composed of CBC, ARS2 and PHAX, and show that both CBCAP and CBC-ARS2 complexes can be reconstituted from recombinant proteins. ARS2 stimulates PHAX binding to the CBC and snRNA 3'-end processing, thereby coupling maturation with export. In vivo, CBC and ARS2 bind similar capped noncoding and coding RNAs and stimulate their 3'-end processing. The strongest effects are for cap-proximal polyadenylation sites, and this favors premature transcription termination. ARS2 functions partly through the mRNA 3'-end cleavage factor CLP1, which binds RNA Polymerase II through PCF11. ARS2 is thus a major CBC effector that stimulates functional and cryptic 3'-end processing sites.

SMN - A chaperone for nuclear RNP social occasions?

“…The pre-snRNA transcripts are then exported from the nucleus by a distinct set of factors that includes the cap-binding complex (CBP80 and CBP20), the snRNA-specific export adaptor phosphorylated adaptor RNA export (PHAX), and arsenite resistance 2 (ARS2). 38 These proteins form a link between the 5 0 cap and the export receptor chromosome region maintenance 1 (CRM1/Exportin1), which interacts with nuclear pore proteins to promote export. 39 Various reviews focus on this function of SMN.…”

An end in sight? Xrn2 and transcriptional termination by RNA polymerase II

“…The short nature of RDH and snRNA genes also makes them susceptible to termination via an Ars2-dependent 3ʹ end processing pathway that is not active on longer genes (showing some similarity to Nrd1 termination in budding yeast) [25]. Although the details that connect Ars2 with transcript processing are not fully elucidated, this may support different termination modes.…”

The Diverse Requirements of ARS2 in nuclear cap-binding complex-dependent RNA Processing

“…Immunoprecipitation of either ARS2 or CBP20/80 pulls down a substantially overlapping set of proteins, implying a strong functional overlap [10,11] . This is supported by loss-of-function experiments demonstrating ARS2 and CBP20/80 regulate similar transcripts, and phenotypically resemble one another [10,11] . This review will emphasize the interactions mediated by ARS2, for additional reviews on the CBC please see [24,25] .…”

“…Each of these RNA classes possess unique processing requirements. The interaction between the CBC and processing machinery is necessary for transcription termination, 3'-end formation, exosomal degradation, intranuclear transport, and export into the cytoplasm [2][3][4][5][6][7][8][9][10][11] . Precisely how the cap facilitates these disparate processes and discriminates between transcripts is not known.…”

“…Precisely how the cap facilitates these disparate processes and discriminates between transcripts is not known. The cap-binding protein, ARS2, is a scaffold that interacts constitutively with CBP20/80 and the 5'-end cap to form a complex called CBCA [8,10,11] , which mediates interactions between the cap complex and RNA 3'-end processing, shuttling, exosome, and export machinery. Thus, ARS2 is emerging as a critical factor, physically coupling multiple steps in the life of RNAP II transcripts.…”