L10: Transcriptional Regulation Of Eukaryotic Gene Expression II

Question 1

Coordinated expression of multiple eukaryotic genes

Answer 1

No operons in eukaryotes

Use single gene regulatory protein. Can coordinate expression of several genes.
E.g. glucocorticoid receptor: 3 target genes, each with different bound activator proteins (low level gene expression). Addition of glucocorticoid receptor with bound glucocorticoid hormone, 3 genes expressed at high level. Glucocorticoid receptor cannot bind DNA without hormone

Glucocorticoid receptor + hormone complex: act as a repressor in some cell types. Repressor/activator activity= dependent on other gene regulatory proteins bound at control regions

Question 2

Example of combinatorial gene control in eukaryotes

Answer 2

Gene may respond to many regulatory proteins
Regulatory protein contributes to control of many genes. Some cell specific, most active in cells, tissues, at different times during development

E.g. development. Combinations of few gene regulatory proteins -> generate many cell types and message for cell.

Question 3

RNA pol I

Answer 3

RNA transcribed: pre r-RNA

RNA function: ribosome components, protein synthesis

Question 4

RNA pol II

Answer 4

RNA transcribed: mRNA, snRNA, miRNA

RNA function: encodes protein, RNA splicing, post-transcriptional gene control

Question 5

RNA pol III

Answer 5

RNA transcribed: tRNA, 5S rRNA, snRNA U6, 7S RNA

RNA function: protein synthesis, ribosome component, RNA splicing, signal-recognition particle for insertion of polypeptides into ER

Promoter regions within transcribed sequences. A&B boxes: promoter elements, in all tRNA genes. C box: promoter element, in 5S rRNA gene

3 GTFs: required to initiate transcription in vitro. TFIIIB, TFIIIC: all tRNA and 5S rRNA genes. TFIIIA: only 5S rRNA gene. TFIIIB: has TBP, must bind before RNA pol III binds

Question 6

Eukaryotic nuclear RNA polymerases

Answer 6

Have 5 core subunits homologous to those of E.coli pol (indicates early evolutionary origin and conservation. Fundamental role- copying DNA into RNA)

Additional 4 small subunits common to all eukaryotic, but not bacterial RNA polymerase

Enzyme-specific subunits

Question 7

Transcription of Human Mitochondrial DNA

Answer 7

Mitochondrial genome reduced compared to ancestral endosymbiont

Genome: circular, ds molecule. Heavy strand (encode most genes) & light strand. Strands transcribed in opp directions, as single transcript from single promoter -> processed into mRNAs, tRNAs, rRNAs

Mitochondrial RNA pol: sing subunit protein, bacteriophage-type RNA pol (transcribed and gene encoded in nucleus, mRNA translated cytoplasm, protein imported into mitochondrial matrix)

2 transcription initiation factors: TFB2M, TFAM (involved in placing mitochondrial RNA pol at promoters: Light strand promoter & heavy strand promoter 1 and in melting the DNA for start of transcription)

For functional mitochondrion: need mitochondrial gene transcription coordinated with expression of nuclear-encoded mitochondrial proteins

Question 8

Transcription of Higher Plant Chloroplast DNA

Answer 8

Chloroplast genome reduced compared to ancestral endosymbiont
Genome: circular, ds molecule
Strands transcribed in opp directions
Multiple promoters
Genes transcribed in groups. Processed into mRNAs, tRNAs, rRNAs

For functional chloroplast: need chloroplastic gene transcription coordinated with expression of nuclear encoded chloroplast proteins

Question 9

Nuclear-encoded pol (NEP)

Answer 9

Involved in transcription of higher plant chloroplast

Single subunit protein (RpoTp gene)

Bacteriophage-type RN pol

Transcribed in nucleus, mRNA translated in cytoplasm, protein imported into chloroplast stroma

Promoters resemble mitochondrial promoters

No known proteins involved in promoter recognition & transcription initiation

Transcribes different genes than PEP

Transcribes 3 of 4 core subunits of PEP

Question 10

Chloroplast-encoded polymerase (PEP)

Answer 10

Involved in transcription of higher plant chloroplast DNA

Multi-subunit protein

Bacterial type RNA pol

Associated with sigma-like factors. Expressed at different time and under different environmental conditions, recognise -35 and -10 sequences found in bacterial promoters & contribute to melting of DNA

Transcribes most chloroplast genes