 <unk> export proteins exist for translocation of mature mRNA and tRNA to the cytoplasm after post @-@ transcriptional modification is complete . This quality @-@ control mechanism is important due to these molecules ' central role in protein translation . <unk> @-@ expression of a protein due to incomplete excision of exons or mis @-@ incorporation of amino acids could have negative consequences for the cell ; thus , incompletely modified RNA that reaches the cytoplasm is degraded rather than used in translation . 
