Gene Structure

Topics to be Covered Introduction Gene structure Promoter Terminator Splice site

Terminology Genome – entire genetic material of an individual Transcriptome – set of transcribed sequences Proteome – set of proteins encoded by the genome

Terminology Only one strand of DNA serves as a template for transcription. Different genes are transcribed from different strands

From Gene to Protein

Eukaryotic Gene Structure 5’ - Promoter Exon1 Intron1 Exon2 Terminator – 3’ UTR splice splice UTR transcription Poly A translation protein

Prokaryotic Gene Structure Promoter CDS Terminator UTR UTR Genomic DNA transcription mRNA translation protein

Topics to be Covered Introduction Gene structure Promoter Terminator Splice sites

Promoter Promoter determines: Which strand will serve as a template. Transcription starting point. Strength of polymerase binding. Frequency of polymerase binding.

Prokaryotic Promoter One type of RNA polymerase. Pribnow box located at –10 (6-7bp) –35 sequence located at -35 (6bp)

Eukaryote Promoter 3 types of RNA polymerases are employed in transcription of genes: RNA polymerase I transcribes rRNA RNA polymerase II transcribes all genes coding for polypeptides RNA polymerase III transcribes small cytoplasmatic RNA, such as tRNA.

Eukaryote Promoter Goldberg-Hogness or TATA located at –30 Additional regions at –100 and at –200 Possible distant regions acting as enhancers or silencers (even more than 50 kb).

Promoter Promoters sequences can vary tremendously. RNA polymerase recognizes hundreds of different promoters

Promoter Strong promoter resemble the consensus sequence. Mutations at promoter sites can influence transcription. Human gene Beta globin

Promoter Conclusions: Promoters are very hard to predict. Promoter prediction must be organism-dependent (and even polymerase-dependent).

Termination Sites The newly synthesized mRNA forms a stem and loop structure (lollipop). A disassociation signal at the end of the gene that stops elongating and releases RNA polymerase. All terminators (eukaryotes and prokaryotes) form a secondary structure.

Termination Sites The terminator region pauses the polymerase and causes disassociation.

Splice Sites Eukaryotics only Removing internal parts of the newly transcribed RNA. Takes place in the cell nucleus (hnRNA)

Splice Sites Conserved splice sites are shared by both the exon and the intron. Different signals on the donor site (3’) and on the acceptor site (5’).

Splice Sites

Alternative splicing Different splice patterns from the same hnRNA sequence. Different products from the same gene Different organs, different stages of development in the same cell. Exact splice sites are difficult to predict