Abstract
Telomerase RNA (TER) is an essential component of the telomerase ribonucleoprotein complex. The mechanism for TER 3′-end processing is highly divergent among different organisms. Here we report a unique spliceosome-mediated TER 3′-end cleavage mechanism in Neurospora crassa which is distinct from that found specifically in the fission yeast Schizosaccharomyces pombe. While the S. pombe TER intron contains the canonical 5′-splice site GUAUGU, the N. crassa TER intron contains a non-canonical 5′-splice site AUAAGU that alone prevents the second step of splicing and promotes spliceosomal cleavage. The unique N. crassa TER 5′-splice site sequence is evolutionarily conserved in TERs from Pezizomycotina and early branching Taphrinomycotina species. This suggests that the widespread and basal N. crassa-type spliceosomal cleavage mechanism is more ancestral than the S. pombe-type. The discovery of a prevalent, yet distinct, spliceosomal cleavage mechanism throughout diverse fungal clades furthers our understanding of TER evolution and non-coding RNA processing.
Highlights
Telomerase RNA (TER) is an essential component of the telomerase ribonucleoprotein complex
The core telomerase ribonucleoprotein (RNP) enzyme is composed of the catalytic telomerase reverse transcriptase (TERT) and telomerase RNA (TER) that contains a short region as the template for telomeric DNA repeat synthesis[2]
The 30-end of the mature NcrTER was determined by rapid amplification of cDNA ends (RACE) from total RNA treated with poly(A) polymerase (Fig. 1a, lane 1)
Summary
Telomerase RNA (TER) is an essential component of the telomerase ribonucleoprotein complex. The unique N. crassa TER 50-splice site sequence is evolutionarily conserved in TERs from Pezizomycotina and early branching Taphrinomycotina species This suggests that the widespread and basal N. crassa-type spliceosomal cleavage mechanism is more ancestral than the S. pombe-type. The N. crassa–type TER spliceosome-mediated 30-end cleavage relies exclusively on a unique 50-SS AUAAGU, which alone is necessary and sufficient for inhibiting the second transesterification step in splicing. The N. crassa-type TER intron is pervasive across Ascomycota, found universally in TERs from filamentous fungi and select early branching fission yeasts This preponderance and conservation among distinct, evolutionary distant and basal fungal species suggest that this mechanism is more ancestral than the S. pombe-type. The discovery of a unique spliceosome-mediated cleavage mechanism provides new insights into TER biogenesis and evolution
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