Ruslan Afasizhev
Boston University School of Dental Medicine, USA
Title: Uridylation-induced RNA degradation in mitochondria of trypanosomes: mechanisms, targets and evolution
Biography
Biography: Ruslan Afasizhev
Abstract
Massive U-insertion/deletion mRNA editing in mitochondria of trypanosomes inspired earlier efforts to discover enzymes
responsible for RNA uridylation. Studies of RNA editing ultimately led to identification of two terminal uridyltransferases
(TUTases): RNA editing TUTase 1 (RET1) and RNA editing TUTase 2 (RET2). Subsequent work demonstrated that RET2
functions as subunit of the RNA editing core complex and is responsible for internal mRNA editing. Conversely, RET1 was
implicated in 3' modification of mRNA, rRNA and guide RNAs. Recently, we identified a protein complex composed of RET1
TUTase, DSS1 3'-5' exonuclease and three additional subunits. This complex, termed mitochondrial 3' processome (MPsome),
is responsible for primary uridylation of ~800-nt gRNA precursors, their processive degradation to a mature size of 40-60
nucleotides and secondary U-tail addition. Both strands of the gRNA gene are transcribed into sense and antisense precursors
of similar lengths. Head-to-head hybridization of these transcripts blocks symmetrical 3'-5' degradation at a fixed distance
from the double-stranded region. Together, our findings suggest a model in which gRNA is derived from the 5' extremity of
a primary molecule by uridylation-induced, antisense transcription-controlled 3'-5' exonucleolytic degradation. Remarkably,
we also established that MPsome-catalyzed 3'-5' degradation also represents the major pathway for mRNA processing and
degradation. These finding poses a logistical challenge to the established paradigm of multicistronic mitochondrial transcription
and raises the questions of mRNA 5' end modification and 3' end definition. We will discuss potential existence of gene specific
promoters and the role of MERS1 NUDIX hydrolase in mRNA 5' processing and stabilization. We will also present data
demonstrating that, in contact to antisense RNA-based 3' end definition of gRNAs, the mature 3' ends of pre-mRNAs are
generated by protein-based mechanism that blocks the MPsome and stimulates mRNA polyadenylation.