[摘要]：Posttranscriptional regulatory mechanisms superimpose "fine-tuning" control upon "on-off" switches characteristic of gene transcription. We have exploited computational modeling with experimental validation to resolve an anomalous relationship between mRNA expression and protein synthesis. The GAIT (gamma-interferon-activated inhibitor of translation) complex repressed VEGF-A synthesis to a low, constant rate independent of VEGF-A mRNA expression levels. Dynamic model simulations predicted an inhibitory GAIT-element-interacting factor to account for this relationship and led to the identification of a truncated form of glutamylprolyl tRNA synthetase (EPRS), a GAIT constituent that mediates binding to target transcripts. The truncated protein, EPRSN1, shields GAIT-element-bearing transcripts from the inhibitory GAIT complex, thereby dictating a "translational trickle" of GAIT target proteins. EPRSN1 mRNA is generated by poly-adenylation-directed conversion of a Tyr codon in the EPRS-coding sequence to a stop codon (PAY*). Genome-wide analysis revealed multiple candidate PAY* targets, including the authenticated target RRM1, suggesting a general mechanism for production of C terminus-truncated regulatory proteins.
