The MIP-coding transcriptome is enriched in transcripts containing miRNA-binding sites. (A) Human transcripts containing miRNA-binding sites are a preferential source of MIPs. The number of MIPs that derive from miRNA targets was calculated for various datasets: B-LCLs from sibships 1 and 2 (this study), B-LCLs,¹⁹  renal cell carcinomas²⁷  and all human peptides listed in the IEDB.²⁴  A list of 8725 human-protein–coding miRNA targets was extracted from TargetScan.²⁵  Numbers on the bottom indicate the number of entries for each dataset. The number of MIPs that derive from miRNA targets for all datasets was significantly higher than the number of miRNA targets in the human protein coding transcriptome (PCT; ^aP < 2.2 × 10⁻¹⁶, ^bP < 3.3 × 10⁻⁹, ^cP < .01, ^dP < 2.12 × 10⁻⁹, and ^eP < 1.38 × 10⁻⁴ by Fisher exact test). (B) Mouse transcripts containing MREs are preferential sources of MIPs. The number of MIPs that derive from miRNA targets was calculated for various datasets: DCs,¹⁷  thymocytes,¹⁶  and all mouse peptides listed in the IEDB.²⁴  A list of 504 mouse protein-coding miRNA targets was extracted from TargetScan.²⁵  Numbers on the bottom indicate the number of entries for each dataset. The number of MIPs that derive from miRNA targets for all MIP datasets was significantly higher than the number of miRNA targets in the mouse protein coding transcriptome (^aP < 1.0 × 10⁻¹¹ and ^b,cP < 2.2 × 10⁻¹⁶ by Fisher exact test).