Analysis of the Caenorhabditis elegans rpc-1 gene
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In eukaryotes, two large subunits form the core catalytic structure of RNA polymerase III (Pol III), which is conserved in other RNA polymerases, Pol I and Pol II. It has been found that Pol III activity is tightly associated to cell growth. TFIII B has been shown to be one of main mediators in this process. No regulation of the Pol III largest subunit gene has been found. In C. elegans, the rpc-1 gene encodes the largest subunit of Pol III. Here, I identified two critical structural components of RPC-1, Gly644 and Gly1055, whose mutations result in larval lethal arrestment. These two amino acid residues are universally conserved in RNA polymerases, indicating their overall involvement in gene transcription mechanism. Also, I found that maternally inherited, not embryonically expressed, rpc-1 gene products survive early development. Starvation was found to suppress rpc-1 gene expression and re-feeding treatment enhances rpc-1 gene expression rapidly. No similar regulation was detected in genes encoding largest subunits of Pol I and Pol II. This is the first time that rpc-1 gene regulation has been reported. Insulin signaling may not be involved in this regulation. Also, I found that rpc-1 promoter is not ubiquitously active in C. elegans. Using the rpc-1p::gfp transgene, the rpc-1 promoter activity is only detected in a subset of neurons in the head and the tail and the intestine. While starvation silences the rpc-1 promoter activity in most tissues and cells, ASK neurons still show GFP staining in the rpc-1p::gfp transgenic animals, indicating that rpc-1 transcription in ASK neurons is continuously active under starvation conditions. Further studies suggest that TGF-[beta] signaling is involved in mediating the rpc-1 promoter activity in ASK neurons.
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