Topic 30: Ribosome Assembly, RNA Polymerase III Transcription

Be able to describe the general process of ribosomal assembly in eukaryotes, and know locations of assembly

- Ribosomal assembly in eukaryotes involves *chaperone proteins* (not part of the final product) that are lost during maturation steps - RNA Polymerase III participate in transcription of rRNAs --- Some RNAP III Promoters can be found within the coding sequence Summary of Eukaryotic Ribosomal Assembly: In Nucleus: - Transcription of pre-RNAs by RNAP I and RNAP III - Maturation to make rRNAs (last class) - Formation of pre-90s immature particle --- Contains ribosomal and non-ribosomal proteins In Nucleoplasm: - Formation of pre-60s and pre-40s subunits --- Most non-ribosomal proteins shed; rRNA trimming Export to Cytoplasm: - Via use of export factors --- Final maturation (including rRNA trimming), shedding of final non-ribosomal proteins

RNAP I

In eukaryotes, the polymerase that only transcribes ribosomal RNA

RNAP III

In eukaryotic cells, a protein that transcribes DNA to synthesize ribosomal 5S rRNA, tRNA and other small RNAs

Be able to summarize the major characteristics of RNAP III transcription (Distinguish from transcription by RNAP II)

Summary of RNAP III Transcription: - Multiple types of promoters --- some internal to the coding sequence - Transcripts produced are small - Transcripts produced are not translated

RNAP III Promoters

Type I and Type II have promoters that lie wholly within the genes. These Type I and Type II genes include a variety of RNA genes such as tRNA, the 5S RNA subunit of the ribosome, and adenovirus VA RNA genes --- entirely or partly located inside the transcribed DNA sequence (internal or intragenic)