MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression in plants and animals. They bind to complementary sites on target mRNAs to induce cleavage or repression of translation. The study identifies two main types of miRNA target sites: 5' dominant sites, which rely on strong complementarity to the miRNA 5' end, and 3' compensatory sites, which require strong complementarity to the miRNA 3' end when the 5' end is weak. The research shows that miRNAs regulate a large fraction of protein-coding genes, with an average miRNA having approximately 100 target sites. The 3' end of miRNAs is key to target specificity within miRNA families. The study also demonstrates that seed sites, which require minimal 3' pairing, are the most common type of miRNA target site. The findings suggest that miRNA target sites are often not well predicted by current methods due to the complexity of base-pairing requirements. The study provides evidence that miRNA target sites are conserved across species and that the 3' end of miRNAs plays a crucial role in determining target specificity. The results indicate that miRNAs regulate a large fraction of protein-coding genes, with the majority of miRNA target sites being 5' dominant. The study also highlights the importance of 3' pairing in miRNA function and the need for more accurate prediction methods that account for the complex requirements of miRNA-target interactions. The research underscores the significance of miRNA-target interactions in gene regulation and the need for further investigation into the mechanisms underlying these interactions.MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression in plants and animals. They bind to complementary sites on target mRNAs to induce cleavage or repression of translation. The study identifies two main types of miRNA target sites: 5' dominant sites, which rely on strong complementarity to the miRNA 5' end, and 3' compensatory sites, which require strong complementarity to the miRNA 3' end when the 5' end is weak. The research shows that miRNAs regulate a large fraction of protein-coding genes, with an average miRNA having approximately 100 target sites. The 3' end of miRNAs is key to target specificity within miRNA families. The study also demonstrates that seed sites, which require minimal 3' pairing, are the most common type of miRNA target site. The findings suggest that miRNA target sites are often not well predicted by current methods due to the complexity of base-pairing requirements. The study provides evidence that miRNA target sites are conserved across species and that the 3' end of miRNAs plays a crucial role in determining target specificity. The results indicate that miRNAs regulate a large fraction of protein-coding genes, with the majority of miRNA target sites being 5' dominant. The study also highlights the importance of 3' pairing in miRNA function and the need for more accurate prediction methods that account for the complex requirements of miRNA-target interactions. The research underscores the significance of miRNA-target interactions in gene regulation and the need for further investigation into the mechanisms underlying these interactions.