BMSC 220 6a transcription and RNA

production of a particular mRNA from a gene (DNA sequence)

-Response of cells to their environment

-Regulation of cell cycle

• -Distinct activities of different cell types in tissue and organ function
• -Cell differentiation and development

-Heat shock protein genes are expressed when cells exposed to elevated temperatures

Mutations causing a reduction in expression of tumour suppressor genes such as Rb or p53 is a major contributing cause in some cancers

-Mutation that changes the regulation of the human apolipoprotein A-I gene promoter (encodes a serum lipid transport protein) affects blood LDL/HDL ratios

Many genes are expressed only once during the life of an organism, for only a short period of time during embryonic development in only one or a few cell types, yet are critical for proper formation of the adult form

• -principal enzymes responsible for RNA synthesis (transcription)
• –synthesize RNA from a DNA template.
• -complex enzymes made up of multiple polypeptide chains.
• -Do not require a primer sequence to initiate RNA synthesis

• -the DNA sequence with which RNA polymerase and other proteins interact to initiate and regulate transcription of a gene
• -molecular dimmer switch

RNA synthesis using a DNA template

protein synthesis using an mRNA template

Chromatin: In eukaryotes, takes place on DNA that has chromatin (nucleosomes must be displaced), takes place on free DNA in prokaryotes

Compartmentalization:

Extensive RNA Processing

Multiple nuclear RNA polymerases in euk:

• an enzyme that catalyzes the synthesis of RNA from a DNA template. Three different nuclear RNA polymerases each responsible for different cellular RNAs
• RNA polymerase I
• RNA polymerase II
• RNA polymerase III

1

Ribosomal RNA (rRNA): 5.8S, 18S, 28S

ALL Messenger RNAs (mRNAs)

-smallest proportion of RNA but greatest regulatory complexity

-regulatory mechanisms have evolved to ensure that the correct gene is transcribed in the correct cell type at the correct time and in the correct amount

Ribosomal RNA (rRNA): 5S

ALL Transfer RNAs (tRNAs)

90

-term used to denote a specific short sequence of DNA base pairs within a gene promoter for which a specific functional property with respect to regulation of transcription of that particular gene has been ascertained

(also called promoter and enhancer elements) regulate expression of genes

• -combination of DNA sequence element and cis-acting DNA sequences
• -regulate transcription

Genes transcribed by RNA polymerase II contain core promoter elements, including the TATA box  (others also exist), and an initiator (Inr) DNA sequence

transcriptional regulatory sequences that can be located at a significant distance from the promoter.

a gene that researchers attach to a regulatory sequence of another gene of interest

• example:
• -(GFP) causes cells that express it to glow green under blue light

-proteins that are required for RNA polymeraseII to initiate transcription.

• -General transcription factors
• -gene-specific transcription factors

• -involved in transcription from all polymerase II promoters.
• -constitute part of the basic (or general) transcription machinery
• -involved in formation of the transcription initiation complex

-Found in the core or basal promoter

• -transcription factors that are not part of the general machinery.
• -bind to promoter and enhancer elements (with specific DNA sequences) of one or a small number of different genes,
• -direct activity of the general transcription factors

-found in upstream promotor

by either

-modifying the rate of transcription initiation by the basal transcription complex,

and/or

-the rate of basal transcription complex assembly

core or basal promoter

a regulatory DNA sequence found in the promoters of many eukaryotic genes transcribed by RNA polymerase II

is a basal transcription factor that binds directly to the TATA box (DNA sequence-specific binding properties).

• polypeptides associated with TBP in the general transcription factor, TFIID.
• (transcription factor II D)

associates with TFIID at the core promoter,

• -TBP binds to the TATA box
• -TFIID associates with TBP
• -TFIIB associates with TFIID
• -Recruitment of RNA polymerase and TFIIF
• -Binding TFIIE and TFIIH

-binding sites for gene specific transcription factors that modulate activity of the basal transcription complex

-same as enhancers

6–10

• SP1
• CBTF

a combination of transcription factors interacting at a specific gene’s promoter/enhancer sequences at any one point in time

a method used to isolate transcription factors based on their binding to specific DNA sequences in order to study them further

(contain a zinc finger domain) are transcription factors that regulate gene transcription in response to hormones such as estrogen and testosterone

(contain a helix-turn-helix DNA binding domain) play critical roles in the regulation of gene expression during embryonic development.

• -a gene that is easily visualized (once it is translated into a protein) whose gene sequence is placed upstream of the gene whose expression you actually want to visualize
• -sometimes placed using plasmids