Regulation and Complexity of Eukaryotic Gene Expression

1. Chapter 19 Organization and Regulation of the Eukaryotic Genome

2. Eukaryotic gene expression • Much more complex than prokaryotic • Larger number of interacting proteins • Placement of transcription/translation lends itself to more opportunities for regulation. • More DNA • Flexible control needed for complex programs and multiple tissue types.

4. Transcription Factors General – • Groups of proteins necessary for recruitment of RNA polymerase and transcription apparatus • Do not increase rate of transcription

5. Specific – • Tissue or time dependent manner to stimulate higher levels of transcription above the base rate • Referred to as activators • Contain a DNA binding domain and a separate acting domain that interacts with the transcription apparatus.

6. Promoters • Form binding sites for general transcrption factors • Mediate the binding of RNA polymerase

7. Enhancers • Contain binding sites for specific transcription factors • Act over long distances by triggering DNA to bend forming loops • This positions the enhancer closer to the promoter.

11. Chromosome structure • Composed of a DNA-protein complex called chromatin. • Euchromatin/heterochromatin • During preparation for mitosis, the chromatin becomes condensed down into linear chromosomes = “packing”

12. Chromatin packing • Histones are proteins responsible for the 1st level of chromatin packing. • DNA becomes wound around this histone core to form  nucleosome (“bead”)

15. Eukaryotic regulation Accomplished through – • DNA structure modification • Transcriptional level • Post-transcription level

16. Gene Regulation via Structure • Most cells within an organism contain the same set of genetic instructions, but the differential expression of specific genes determines the specialization of the cells. 3 ways to regulate via structure: • Histone modification • DNA methylation

19. Regulation at the Transcription level • Regulating gene expression at the transcription level is the most important and universally used stage. • transcription factors, associated with most eukaryotic genes, help regulate transcription by binding certain proteins. • This process aids in the precise regulation of gene expression.

20. numerous in eukaryotes • necessary for assembly of the “transcription initiation complex” • necessary for recruitment of RNA polymerase to bind to promoter • necessary for initiation of transcription (but do not increase the base rate of transcription)

22. Post transcriptional miRNA (microRNA’s) • arise from a small, single stranded RNA encoded genes in the nucleus. • formed from a precursor molecule, diced into fragments and associated with a protein complex. • binds to a complementary mRNA sequence and either degrades the target or blocks translation.

24. small interfering RNA (siRNA’s) • similar to miRNA’s but arise form a long, double stranded RNA • can come from either the cell or outside of the cell.