Ruf 7 - Main Points: Lecture 6 Gene density as a function...

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Main Points: Lecture 6 Gene density as a function of organism complexity 3 classes of DNA in eukaryotes: How was this determined? Chromatin: highly organized DNA-protein complex Nucleosome as the basic unit of organization: histone octamer + 146bp DNA Various stages of chromatin packing Euchromatin vs. heterochromatin
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Eukaryotic RNA Polymerase and the Transcription Control Sequences are Different From those in Prokaryotic Genomes Eukaryotic polymerases are multi-subunit complexes: 12-16 subunits Eukaryotic DNA polymerases do not directly bind to promoter containing DNA- ancillary factors perform this function There are 3 distinct RNA polymerase enzymes with distinct gene class specificities Pol I: rRNA Pol II: pre-mRNAs , some small non-coding RNAs Pol III: tRNAs, other small RNAs Originally defined by sensitivity to α-amanitin
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α -amanitin concentration tRNAs (+ others) 28s rRNA 18s rRNA 0 1 Low 2 Med. 3 High 4 total RNA Large Small Neg (-) Pos. (+) mRNAs Three Eukaryotic RNA polymerases: Classified by sensitivity to α -amanitin
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Type RNA class α -amanitin sensitivity RNA Pol I rRNA only Only very high levels RNA Pol II Pre mRNAs and a few small (non protein coding) RNAs Very low levels RNA Pol III tRNA and other small RNAs Intermediate levels Three Eukaryotic RNA Polymerases First Classified by α -aminitin sensitivity
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Minimal Pol II Promoter: has only 2 elements TATAA…….N 20 ……YYCAYYYYY…. N 24 …..AGAC Startpoint TATA Box InR DPE Initiator element Downstream Promoter Element TATA + InR: TATA Box containing core promoters InR + DPE: TATA-less core promoters
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Sequential assembly of the general
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Ruf 7 - Main Points: Lecture 6 Gene density as a function...

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