Many eukaryotes initiate pathways of Argonaute-bound small RNA (sRNA) production with a step that specifically targets sets of aberrant and/or otherwise deleterious transcripts for recognition by an RNA-dependent RNA polymerase complex (RDRC). The biogenesis of 23- to 24-nt sRNAs in growing Tetrahymena occurs by physical and functional coupling of the growth-expressed Dicer, Dcr2, with one of three RDRCs each containing the single genome-encoded RNA-dependent RNA polymerase, Rdr1. Tetrahymena RDRCs contain an active uridylyltransferase, either Rdn1 or Rdn2, and Rdn1 RDRCs also contain the Rdf1 and Rdf2 proteins. Although Rdn2 is nonessential and RDRC-specific, Rdn1 is genetically essential and interacts with a non-RDRC protein of 124 kDa. Here we characterize this 124-kDa protein, designated RNA silencing protein 1 (Rsp1), using endogenous locus tagging, affinity purification, and functional assays, as well as gene-knockout studies. We find that Rsp1 associates with Rdn1-Rdf1 or Rdn1-Rdf2 subcomplexes as an alternative to Rdr1, creating Rsp1 complexes (RSPCs) that are physically separate from RDRCs. The uridylyltransferase activity of Rdn1 is greatly reduced in RSPCs compared with RDRCs, suggesting enzyme regulation by the alternative partners. Surprisingly, despite the loss of all known RDRC-generated classes of endogenous sRNAs, RSP1 gene knockout was tolerated in growing cells. A minority class of Dcr2-dependent sRNAs persists in cells lacking Rsp1 with increased size heterogeneity. These findings bring new insights about the essential and nonessential functions of RNA silencing in Tetrahymena, about mechanisms of endogenous small interfering RNA production, and about the roles of cellular uridylyltransferases.
We investigated the role of cholinergic neurotransmission in olfactory fear learning. Mice receiving pairings of odor and foot shock displayed fear to the trained odor the following day. Pretraining injections of the nicotinic antagonist mecamylamine had no effect on subsequent freezing, w ... more
In Aplysia, repeated trials of aversive stimuli produce long-term sensitization (LTS) of defensive reflexes and suppression of feeding. Whereas the cellular underpinnings of LTS have been characterized, the mechanisms of feeding suppression remained unknown. Here, we report that LTS traini ... more
The anaphase promoting complex/cyclosome (APC/C) is an E3 ligase regulated by Cdh1. Beyond its role in controlling cell cycle progression, APC/C–Cdh1 has been detected in neurons and plays a role in long-lasting synaptic plasticity and long-term memory. Herein, we further examined the role ... more
The human mouth is home to a teeming community of microbes, yet still relatively little is known about what determines the specific types of microorganisms that live there. Is it your genes that decide who lives in the microbial village, or is it your environment? In a study published in ... more
Your genes determine much about you, but environment can have a strong influence on your genes even before birth, with consequences that can last a lifetime. In a study published in Genome Research, researchers have for the first time shown that the environment experienced in the womb defi ... more
The human gut is home to a teeming ecosystem of microbes that is intimately involved in both human health and disease. But while the gut microbiota is interacting with our body, they are also under constant attack from viruses. In a study published in Genome Research, researchers have ana ... more