Truncated forms of U2 snRNA (U2-tfs) are shunted toward a novel uridylylation pathway that differs from the degradation pathway for U1-tfs

Hideaki Ishikawa, Yuko Nobe, Keiichi Izumikawa, Masato Taoka, Yoshio Yamauchi, Hiroshi Nakayama, Richard J Simpson, Toshiaki Isobe, Nobuhiro Takahash
2017 Figshare  
During the biogenesis of U1 small nuclear ribonucleoprotein, a small population of U1 snRNA molecules acquires an extra methylation at the first transcribed nucleotide and a nucleolytic cleavage to remove the 3′ structured region including the Sm protein–binding site and stem-loop 4. These modifications occur before hypermethylation of the monomethylated 5′ cap, whereby producing truncated forms of U1 snRNA (U1-tfs) that are diverted from the normal pathway to a processing body–associated
more » ... dy–associated degradation pathway. Here, we demonstrate that a small population of U2 snRNA molecules receives post-transcriptional modifications similar to those of U1 to yield U2-tfs. Like U1-tfs, U2-tfs molecules were produced from transcripts of the U2 snRNA gene having all cis-elements or lacking the 3′ box. Unlike U1-tfs, however, a portion of U2-tfs received additional uridylylation of up to 5 nucleotides in length at position 87 (designated as U2-tfs-polyU) and formed an Sm protein–binding site–like structure that was stabilized by the small nuclear ribonucleoprotein SmB/B' probably as a part of heptameric Sm core complex that associates to the RNA. Both U2-tfs and U2-tfs-polyU were degraded by a nuclease distinct from the canonical Dis3L2 by a process catalyzed by terminal uridylyltransferase 7. Collectively, our data suggest that U2 snRNA biogenesis is regulated, at least in part, by a novel degradation pathway to ensure that defective U2 molecules are not incorporated into the spliceosome.
doi:10.6084/m9.figshare.5629984.v1 fatcat:s6wvdqtd2raz5oym4q4h3ncmcm