InterPro domain: IPR040402

Higher plants have five multi-subunit nuclear RNA polymerases: RNAP I, RNAP II and RNAP III, which are essential for viability; plus the non-essential polymerases IVa and V (IVb), which specialize in small RNA-mediated gene silencing pathways. RNAP IVa and/or RNAP IVb might be involved in RNA-directed DNA methylation of endogenous repetitive elements, silencing of transgenes, regulation of flowering-time genes, inducible regulation of adjacent gene pairs, and spreading of mobile silencing signals [ 1 , 2 , 3 ].

NRPD1a is the largest subunit of RNAP IVa, whereas NRPD1b is the largest subunit of RNAP V/IVb. The full subunit compositions of RNAP IVa and RNAP V/IVb are not known, nor are their templates or enzymatic products. However, it has been shown that RNAP IVa and, to a lesser extent, RNAP V/IVb are crucial for several RNA-mediated gene silencing phenomena [ 4 ].

This entry represents the C-terminal domain found in NRPD1a and NRPD1b.

1. Roles of RNA polymerase IV in gene silencing. Trends Plant Sci. 13, 390-7
2. Finding the right template: RNA Pol IV, a plant-specific RNA polymerase. Mol. Cell 17, 754-6
3. Noncoding transcription by RNA polymerase Pol IVb/Pol V mediates transcriptional silencing of overlapping and adjacent genes. Cell 135, 635-48
4. NRPD1a and NRPD1b are required to maintain post-transcriptional RNA silencing and RNA-directed DNA methylation in Arabidopsis. Plant J. 55, 596-606