Abstract
The telomerase holoenzyme is critical for maintaining eukaryotic genome integrity. In addition to a reverse transcriptase and an RNA template, telomerase contains additional proteins that protect the telomerase RNA and promote holoenzyme assembly. Here we report that the methyl phosphate capping enzyme (MePCE) Bmc1/Bin3 is a stable component of the S. pombe telomerase holoenzyme. Bmc1 associates with the telomerase holoenzyme and U6 snRNA through an interaction with the recently described LARP7 family member Pof8, and we demonstrate that these two factors are evolutionarily linked in fungi. Our data suggest that the association of Bmc1 with telomerase is independent of its methyltransferase activity, but rather that Bmc1 functions in telomerase holoenzyme assembly by promoting TER1 accumulation and Pof8 recruitment to TER1. Taken together, this work yields new insight into the composition, assembly, and regulation of the telomerase holoenzyme in fission yeast as well as the breadth of its evolutionary conservation.
Highlights
The telomerase holoenzyme is critical for maintaining eukaryotic genome integrity
While Bmc1/methyl phosphate capping enzyme (MePCE) is conserved in many eukaryotes, its presence in the fission yeast S. pombe, an organism lacking 7SK snRNA27,30, is not well understood
Since our results indicate that Bmc[1] interacts with the mature form of TER1, we set out to confirm the presence of Bmc[1] in the S. pombe telomerase holoenzyme
Summary
In addition to a reverse transcriptase and an RNA template, telomerase contains additional proteins that protect the telomerase RNA and promote holoenzyme assembly. Eukaryotes extend telomeric DNA sequences through the telomerase holoenzyme, a complex containing the telomerase reverse transcriptase (Trt[1] in the fission yeast Schizosaccharomyces pombe), an RNA template (TER1 in S. pombe), and accessory proteins that promote complex assembly and tethering to telomeric DNA1–5. In contrast to ciliate telomerase RNAs, which are small RNA polymerase III transcripts[6], yeast and metazoan telomerase RNAs are longer and transcribed by RNA polymerase II as precursors[7,8] These precursors undergo an extensive maturation process to yield the mature form that integrates into the telomerase holoenzyme[3,4,7,8]. The Sm complex is replaced by the Lsm[2-8] complex, which serves to protect the mature 3’ end of TER1 from exonucleolytic degradation and promotes the interaction between TER1 and Trt[1] in the active telomerase holoenzyme. The switch from the Sm to Lsm complexes correlates with distinct, nonoverlapping substrates: TER1 precursors are exclusively bound by the Sm complex, while the mature form of TER1, ending in a polyuridylate stretch upstream the spliceosomal cleavage site, is only bound by the Lsm[2-8] complex[10]
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