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Abstract:
Messenger RNA (mRNA) synthesis and export are tightly linked, but the molecular mechanisms of this coupling are largely
unknown. In Saccharomyces cerevisiae, the conserved TREX complex couples transcription to mRNA export and mediates
mRNP formation. Here, we show that TREX is recruited to the transcription machinery by direct interaction of its
subcomplex THO with the serine 2-serine 5 (S2/S5) diphosphorylated CTD of RNA polymerase II. S2 and/or tyrosine 1 (Y1)
phosphorylation of the CTD is required for TREX occupancy in vivo, establishing a second interaction platform necessary for
TREX recruitment in addition to RNA. Genome-wide analyses show that the occupancy of THO and the TREX components
Sub2 and Yra1 increases from the 59 to the 39 end of the gene in accordance with the CTD S2 phosphorylation pattern.
Importantly, in a mutant strain, in which TREX is recruited to genes but does not increase towards the 39 end, the expression
of long transcripts is specifically impaired. Thus, we show for the first time that a 59-39 increase of a protein complex is
essential for correct expression of the genome. In summary, we provide insight into how the phospho-code of the CTD
directs mRNP formation and export through TREX recruitment.
