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Abstract
<p id="P1">Many eukaryotic genes generate linear mRNAs and circular RNAs, but it is
largely unknown
how the ratio of linear to circular RNA is controlled or modulated. Using RNAi screening
in
<i>Drosophila</i> cells, we identify many core spliceosome and transcription termination
factors that
control the RNA outputs of reporter and endogenous genes. When spliceosome components
were depleted or inhibited pharmacologically, the steady-state levels of circular
RNAs increased while expression of their associated linear mRNAs concomitantly decreased.
Upon inhibiting RNA polymerase II termination via depletion of the cleavage/polyadenylation
machinery, circular RNA levels were similarly increased. This is because readthrough
transcripts now extend into downstream genes and are subjected to backsplicing. In
total, these results demonstrate that inhibition or slowing of canonical pre-mRNA
processing events shifts the steady-state output of protein-coding genes towards circular
RNAs. This is in part because nascent RNAs become directed into alternative pathways
that lead to circular RNA production.
</p><p id="P2">Many protein-coding genes produce linear mRNAs and circular RNAs. Liang
et al. find
that circular RNAs become the preferred gene output when core spliceosome or transcription
termination factors are depleted from cells. This is in part because nascent RNAs
are directed into alternative pathways that lead to circular RNA biogenesis.
</p><p id="P3">
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