The lin-4 regulatory RNA controls developmental timing in Caenorhabditis elegans by blocking LIN-14 protein synthesis after the initiation of translation

lin-4 encodes a small RNA that is complementary to sequences in the 3' untr anslated region (UTR) of lin-14 mRNA and that acts to developmentally repre ss the accumulation of LIN-14 protein. This repression is essential for the proper timing of numerous events of Caenorhabditis elegans larval developm ent. We have investigated the mechanism of lin-4 RNA action by examining th e fate of lin-14 mRNA in vivo during the time that lin-4 RNA is expressed. Our results indicate that the rate of synthesis of lin-14 mRNA, its state o f polyadenylation, its abundance in the cytoplasmic fraction, and its polys omal sedimentation profile do not change in response to the accumulation of lin-4 RNA. Our results indicate that association of lin-4 RNA with the 3' UTR of lin-14 mRNA permits normal biogenesis of lin-14 mRNA, and normal tra nslational initiation, but inhibits step(s) thereafter, such as translation al elongation and/or the release of stable LIN-14 protein. (C) 1999 Academi c Press.