Similarities between Argonautes and the alpha-sarcin-like ribotoxins: Implications for microRNA action.
We report structural, functional, and biochemical similarities between Argonautes, the effector proteins of RNA-induced silencing complexes (RISCs), and alpha-sarcin-like ribotoxins. At the structural level, regions of similarity in the amino acid sequence are located in protein loops both in the ribotoxins and in the Argonautes. In ribotoxins, these protein loops confer specificity for a highly conserved segment of ribosomal RNA, the Sarcin-Ricin-Loop (SRL) that undergoes cleavage by the ribotoxin ribonuclease. This leads to suppression of translation. In addition to the structural similarity with ribotoxins, the Argonaute proteins (Ago) show both functional and biochemical parallels. Like the ribotoxins, the Agos exhibit ribonuclease activity and like the ribotoxins, translational suppression mediated by miRISC-resident Ago is accompanied by intact polysomes. Furthermore, in both translationally suppressed systems, the puromycin reaction, reflecting correct translocation and peptidyl-transferase activities, is unharmed. These findings support a mechanism for Ago-miRISCs whereby regulated cleavage of ribosomal RNA leads to translational suppression.
Department of Cell Research and Immunology, Tel Aviv University, Ramat Aviv 69978, Israel.
Edward
E
Pichinuk
Daniel H
DH
Wreschner
D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D002417:Cattle; D017124:Conserved Sequence; D004722:Endoribonucleases / Q000737:chemistry* / Q000378:metabolism; D039642:Eukaryotic Initiation Factors / Q000737:chemistry* / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D051379:Mice; D035683:MicroRNAs / Q000737:chemistry / Q000378:metabolism; D008957:Models, Genetic; D008958:Models, Molecular; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D011691:Puromycin; D012323:RNA Processing, Post-Transcriptional; D012335:RNA, Ribosomal / Q000378:metabolism; D034743:RNA-Induced Silencing Complex / Q000737:chemistry* / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D001426:Bacterial Proteins; D039642:Eukaryotic Initiation Factors; D005656:Fungal Proteins; D035683:MicroRNAs; D012335:RNA, Ribosomal; D034743:RNA-Induced Silencing Complex; C014801:alpha-sarcin; D011691:Puromycin; D004722:Endoribonucleases