miRNPs are a novel class of ribonucleoproteins containing numerous microRNAs (miRNAs). Gemin3, a DEAD-box RNA helicase, binds to the Survival of Motor Neurons (SMN) protein and is a component of the SMN complex, which also includes Gemin2, Gemin4, Gemin5, and Gemin6. Reduction in SMN protein causes Spinal muscular atrophy (SMA), a neurodegenerative disease. The SMN complex is involved in the assembly and restructuring of diverse ribonucleoprotein (RNP) complexes. This study reports that Gemin3 and Gemin4 are part of a separate complex containing eIF2C2, a member of the Argonaute protein family. This complex is a large ~15S RNP containing numerous miRNAs. The researchers identified 40 miRNAs, some of which are similar to recently described human miRNAs. Genomic sequences suggest that miRNAs are derived from larger precursors capable of forming stem-loop structures. The study shows that miRNAs are associated with the Gemin3–eIF2C2 complex in vivo. Immunoprecipitation experiments confirmed the presence of miRNAs in this complex. Sedimentation on sucrose gradients revealed that Gemin3, Gemin4, eIF2C2, and miRNAs form large novel RNPs (miRNPs) that sediment at ~15S. The miRNAs identified in this study are derived from novel genes and are predicted to fold into stem-loop structures similar to those of stRNAs. These miRNAs are likely processed from longer precursors by an RNAi-like mechanism. The study also identifies 31 novel miRNAs, some of which are not previously described. The findings suggest that miRNPs are a new class of RNPs containing Gemin3, Gemin4, eIF2C2, and miRNAs. The study highlights the potential regulatory roles of miRNAs and their association with the SMN complex. The results provide insights into the function of miRNAs and their potential involvement in various cellular processes.miRNPs are a novel class of ribonucleoproteins containing numerous microRNAs (miRNAs). Gemin3, a DEAD-box RNA helicase, binds to the Survival of Motor Neurons (SMN) protein and is a component of the SMN complex, which also includes Gemin2, Gemin4, Gemin5, and Gemin6. Reduction in SMN protein causes Spinal muscular atrophy (SMA), a neurodegenerative disease. The SMN complex is involved in the assembly and restructuring of diverse ribonucleoprotein (RNP) complexes. This study reports that Gemin3 and Gemin4 are part of a separate complex containing eIF2C2, a member of the Argonaute protein family. This complex is a large ~15S RNP containing numerous miRNAs. The researchers identified 40 miRNAs, some of which are similar to recently described human miRNAs. Genomic sequences suggest that miRNAs are derived from larger precursors capable of forming stem-loop structures. The study shows that miRNAs are associated with the Gemin3–eIF2C2 complex in vivo. Immunoprecipitation experiments confirmed the presence of miRNAs in this complex. Sedimentation on sucrose gradients revealed that Gemin3, Gemin4, eIF2C2, and miRNAs form large novel RNPs (miRNPs) that sediment at ~15S. The miRNAs identified in this study are derived from novel genes and are predicted to fold into stem-loop structures similar to those of stRNAs. These miRNAs are likely processed from longer precursors by an RNAi-like mechanism. The study also identifies 31 novel miRNAs, some of which are not previously described. The findings suggest that miRNPs are a new class of RNPs containing Gemin3, Gemin4, eIF2C2, and miRNAs. The study highlights the potential regulatory roles of miRNAs and their association with the SMN complex. The results provide insights into the function of miRNAs and their potential involvement in various cellular processes.