Mutations in Conserved Residues of the C. elegans microRNA Argonaute ALG-1 Identify Separable Functions in ALG-1 miRISC Loading and Target Repression

Micrornas function in diverse developmental and physiological processes by regulating target gene expression at the post-transcriptional level. alg-1 is one of two caenorhabditis elegans argonautes (alg-1 and alg-2) that together are essential for microrna biogenesis and function. here,we report the identification of novel antimorphic (anti) alleles of alg-1 as suppressors of lin-28(lf) precocious developmental phenotypes. the alg-1(anti) mutations broadly impair the function of many micrornas and cause dosage-dependent phenotypes that are more severe than the complete loss of alg-1. alg-1(anti) mutant proteins are competent for promoting dicer cleavage of microrna precursors and for associating with and stabilizing micrornas. however,our results suggest that alg-1(anti) proteins may sequester micrornas in immature and functionally deficient microrna induced silencing complexes (miriscs),and hence compete with alg-2 for access to functional micrornas. immunoprecipitation experiments show that alg-1(anti) proteins display an increased association with dicer and a decreased association with ain-1/gw182. these findings suggest that alg-1(anti) mutations impair the ability of alg-1 mirisc to execute a transition from dicer-associated microrna processing to ain-1/gw182 associated effector function,and indicate an active role for alg/argonaute in mediating this transition. © 2014 zinovyeva et al.