Alternative titles; symbolsRNA POLYMERASE III, 32-KD SUBUNIT; RPC32RNA POLYMERASE III, 32-KD SUBUNIT, ALPHARPC32-ALPHARNA POLYMERASE III, SUBUNIT C7; RPC7DNA-DIR...
Alternative titles; symbols
HGNC Approved Gene Symbol: POLR3G
Cytogenetic location: 5q14.3 Genomic coordinates (GRCh38): 5:90,473,928-90,514,556 (from NCBI)
Transcription of nuclear DNA is mediated by RNA polymerases Pol I, Pol II, and Pol III. Pol III specifically directs transcription of small noncoding RNAs that are involved in translation, splicing, and other cellular processes. POLR3G and POLR3GL (617457) are alternative Pol III subunits (Haurie et al., 2010).
▼ Cloning and Expression
Wang and Roeder (1997) cloned human POLR3G, which they called RPC32, from a HeLa cell cDNA library. The deduced 233-amino acid protein has a calculated molecular mass of 27 kD. RPC32 shares 25% identity with its likely yeast ortholog Rpc31, and both proteins contain an acidic C-terminal tail. RPC32 had an apparent molecular mass of 32 kD by 2-dimensional PAGE.
Wong et al. (2011) found that mouse Polr3g was absent from unfertilized oocytes, but was expressed in the cytoplasm of zygotes and 2-cell embryos. Nuclear Polr3g was first detected in 8-to-16-cell mouse embryos and blastocysts. POLR3G was also detected in human embryonic stem cells (ESCs) and in undifferentiated induced pluripotent stem cells.
▼ Gene Function
Using 4M urea or 0.5% sarkosyl, Wang and Roeder (1997) dissociated a subcomplex from the core complex of purified human RNA Pol III. The complex contained RPC32 in addition to RPC62 (POLR3C; 617454) and RPC39 (POLR3F; 617455). The core complex lacking the subcomplex was able to function in transcription elongation and termination, but was not capable of accurate transcription initiation. The natural subcomplex, as well as reconstituted recombinant 3-subunit subcomplex, interacted with initiation factor TFIIIB90 (BRF1; 604902) and TATA-binding protein (TBP; 600075), and when combined with the core RNA Pol III complex, restored accurate transcription initiation.
Haurie et al. (2010) found that purified human RNA Pol III containing RPC32-alpha or RPC32-beta (POLR3GL) subunits had comparable activity in transcribing genes for 5S rRNA (RN5S1; 180420), tRNA-met (see TRNAM1, 180621), adenoviral-associated RNA, and 7SK RNA (RN7SK; 601515). However, knockdown of RPC32-alpha or RPC32-beta in human cell lines via short hairpin RNAs revealed distinct cellular effects. Knockdown of RPC32-alpha in Huh7 hepatocarcinoma cells had little effect, whereas knockdown of RPC32-beta substantially reduced cell growth and dramatically increased cell death. Knockdown of RPC32-alpha in HeLa cells reduced colony formation in soft agar. Overexpression of RPC32-alpha, but not RPC32-beta, enhanced IMR90 human fibroblast transformation, colony formation, and anchorage-independent growth, and enhanced expression of Pol III-transcribed genes. Overexpression of RPC32-alpha, but not RPC32-beta, also significantly increased expression of several Pol III-transcribed genes associated with cell survival, tumor growth, and metastasis, while reducing expression of several genes with tumor suppressor activity. Haurie et al. (2010) concluded that RPC32-beta is a subunit of the general form of human Pol III and is required for cell survival, and that RPC32-alpha functions in undifferentiated ESCs and in transformed cells.
Using short hairpin RNAs, Wong et al. (2011) found that knockdown of POLR3G in human ESCs caused both upregulation and downregulation of Pol III-transcribed genes. Knockdown of POL3G also caused loss of ESC pluripotency and promoted ESC differentiation into mesodermal, endodermal, and ectodermal lineages, with concomitant changes in gene expression. Overexpression of POLR3G rendered ESCs resistant to differentiation into embryoid bodies. Chromatin immunoprecipitation showed that OCT4 (POU5F1; 164177) and NANOG (607937) bound to putative regulatory sequences around the POLR3G transcription start site. Knockdown of OCT4 or NANOG, or inhibition of ERK1 (MAPK3; 601795)/ERK2 (MAPK1; 176948), significantly downregulated POLR3G expression.
Using coimmunoprecipitation and mass spectrometric analysis, Renaud et al. (2014) found that POLR3G and POLR3GL resided in separate purified HeLa cell Pol III complexes. POLR3G and POLR3GL were differentially expressed under different conditions and in different cell types, and POLR3G-containing Pol III was relatively more abundant in dividing cells. However, both interacted with POLR3D (187280) and occupied the same target genes. The POLR3G promoter, but not the POLR2GL promoter, bound the transcription factor MYC (190080).
▼ Gene Structure
Renaud et al. (2014) determined that the POLR3G gene has 7 exons.
Renaud et al. (2014) determined that the POLR3G gene lies in a head-to-head orientation with the MBLAC2 gene (LOC153364) on chromosome 5p14.3.