FACTOID # 21: 15% of Army recruits from South Dakota are Native American, which is roughly the same percentage for female Army recruits in the state.
 
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Encyclopedia > RNA polymerase III

RNA polymerase III (also called Pol III) transcribes DNA to synthesize ribosomal 5S rRNA, tRNA and other small RNAs. The genes transcribed by RNA Pol III fall in the category of "housekeeping" genes whose expression is required in all cell types and most environmental conditions. Therefore the regulation of Pol III transcription is primarily tied to the regulation cell growth and the cell cycle, thus requiring fewer regulatory proteins than RNA polymerase II. Transcription is the process through which a DNA sequence is enzymatically copied by an RNA polymerase to produce a complementary RNA. Or, in other words, the transfer of genetic information from DNA into RNA. In the case of protein-encoding DNA, transcription is the beginning of the process that ultimately... The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid —usually in the form of a double helix— that contains the genetic instructions specifying the biological development of all cellular forms of life, and most viruses. ... A non-coding RNA (ncRNA) is any RNA molecule that functions without being translated into a protein. ... Transfer RNA (abbreviated tRNA) is a small RNA chain (74-93 nucleotides) that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. ... RNA polymerase II (also called RNAP II and Pol II) transcribes DNA to synthesize precursors of mRNA and most snRNA. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase. ...


In the process of transcription (by any polymerase) there are three main stages: Transcription is the process through which a DNA sequence is enzymatically copied by an RNA polymerase to produce a complementary RNA. Or, in other words, the transfer of genetic information from DNA into RNA. In the case of protein-encoding DNA, transcription is the beginning of the process that ultimately...

  1. Initiation; requiring construction of the RNA polymerase complex on the gene's promoter.
  2. Elongation; the writing of the RNA transcript.
  3. Termination; the finishing of RNA writing and disassembly of the RNA polymerase complex.

In genetics, a promoter is a DNA sequence that enables a gene to be transcribed. ...

Pol III Initiation

Initiation: the construction of the polymerase complex on the promoter. Pol III is unusual (compared to Pol II) requiring no control sequences upstream of the gene, instead normally relying on internal control sequences - sequences within the transcribed section of the gene (although upstream sequences are occasionally seen, eg. U6 snRNA gene has an upstream TATA Box as seen in Pol II Promoters).


Typical stages in a tRNA (also termed class II) gene initiation: Transfer RNA (abbreviated tRNA) is a small RNA chain (74-93 nucleotides) that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. ...

  1. TFIIIC (Transcription Factor for polymerase III C) binds to two intragenic (lying within the transcribed DNA sequence) control sequences, the A and B Blocks (also termed box A and box B).
  2. TFIIIC acts as an assembly factor that positions TFIIIB to bind to DNA at a site centered approximately 26 base pairs upstream of the start site of transcription.
  3. TFIIIB (Transcription Factor for polymerase III B), consists of three subunits: TBP (TATA Binding Protein), the Pol II transcription factor TFIIB-related protein, Brf1 (or Brf2 for transcription of a subset of Pol III-transcribed genes in vertebrates) and Bdp1.
  4. TFIIIB is the transcription factor that assembles Pol III at the start site of transcription. Once TFIIIB is bound to DNA, TFIIIC is no longer required. TFIIIB also plays an essential role in promoter opening.

TFIIIB remains bound to DNA following initiation of transcription by Pol III (unlike bacterial σ factors and most of the basal transcription factors for Pol II transcription. This leads to a high rate of transcriptional reinitiation of Pol III-transcribed genes. The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid —usually in the form of a double helix— that contains the genetic instructions specifying the biological development of all cellular forms of life, and most viruses. ... Cartoon of the TATA binding protein structure. ...


Typical stages in 5S rRNA (also termed class I) gene initiation:

  1. TFIIIA (Transcription Factor for polymerase III A) binds to the intragenic (lying within the transcribed DNA sequence) 5S rRNA control sequence, the C Block (also termed box C).
  2. TFIIIA Serves as a platform that that replaces the A and B Blocks for positioning TFIIIC in an orientation with respect to the start site of transcription that is equivalent to what is observed for tRNA genes.
  3. Once TFIIIC is bound to the TFIIIA-DNA complex the assembly of TFIIIB proceeds as described for tRNA transcription.

Typical stages in a U6 snRNA (also termed class III) gene initiation (documented in vertebrates only): The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid —usually in the form of a double helix— that contains the genetic instructions specifying the biological development of all cellular forms of life, and most viruses. ... The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid —usually in the form of a double helix— that contains the genetic instructions specifying the biological development of all cellular forms of life, and most viruses. ...

  1. SNAPc (SNRNA Activating Protein complex) (also termed PBP and PTF) binds to the PSE (Proximal Sequence Element) centered approximately 55 base pairs upstream of the start site of transcription. This assembly is greatly stimulated by the Pol II transcription factors Oct1 and STAF that bind to an enhancer-like DSE (Distal Sequence Element) at least 200 base pairs upstream of the start site of transcription. These factors and promoter elements are shared between Pol II and Pol III transcription of snRNA genes.
  2. SNAPc acts to assemble TFIIIB at a TATA box centered 26 base pairs upstream of the start site of transcription. It is the presence of a TATA box that specifies that the snRNA gene is transcribed by Pol III rather than Pol II.
  3. The TFIIIB for U6 snRNA transcription contains a smaller Brf1 paralogue, Brf2.
  4. TFIIIB is the transcription factor that assembles Pol III at the start site of transcription. Sequence conservation predicts that TFIIIB containing Brf2 also plays a role in promoter opening.

  Results from FactBites:
 
RNA polymerase - Wikipedia, the free encyclopedia (928 words)
RNA polymerase enzymes are essential and are found in all organisms and many viruses.
RNA polymerase I synthesizes a pre-rRNA 45S, which matures into 28 S, 18S and 5,8S rRNAs which will form the major RNA sections of the ribosome.
RNA polymerase III synthesizes tRNAs, rRNA 5S and other small RNAs found in the nucleus and cytosol.
RNA polymerase III - Wikipedia, the free encyclopedia (676 words)
The genes transcribed by RNA Pol III fall in the category of "housekeeping" genes whose expression is required in all cell types and most environmental conditions.
Therefore the regulation of Pol III transcription is primarily tied to the regulation cell growth and the cell cycle, thus requiring fewer regulatory proteins than RNA polymerase II.
TFIIIB (Transcription Factor for polymerase III B), consists of three subunits: TBP (TATA Binding Protein), the Pol II transcription factor TFIIB-related protein, Brf1 (or Brf2 for transcription of a subset of Pol III-transcribed genes in vertebrates) and Bdp1.
  More results at FactBites »

 
 

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