Primary step for controlling gene expression
Initiation of transcription

Features of prok gene expression
Genes are organized into operons; Coupled transcription and translation.

Stages of transcription
Initiation, Elongation, Termination, Processing

The strands of DNA during transcription are denoted by these names
Template strand (actually bound by RNA Pol) and the Sense strand whose sequences are written for the DNA of genes.

One of the largest enzymes in the cell
RNA Pol

Number of copies of RNA Pol per cell
About 3000

The typical layout of a prokaryotic promoter sequence
5'-....-35_region..........-10_region...+1 purine(A/G)....-3' .  The -35 region is the TTGACAT box, and the -10 region is the TATA box.

Strong promoters do this:
Match consensus sequence; bind the holoenzyme tightly; initiate often, genes highly epxressed.

Weak promoters do this:
Many differences from consensus sequence; bind the holoenzyme loosely; initiate rarely, genes poorly expressed.

One way viruses regulate transcription
They supply a viral sigma subunit

The second layer of regulation
Transcription factors

Rho dependent termination
Protein (rho) actively disrupts RNA Pol

Rho independent termination
GC-rich hairpin forms, strains RNA-DNA hybrid, causing RNA Pol to fall off

Eukaryotic transcription strategy
multicellular, stable env; tissue-specific gene expression rather than env-specific; accomplish developmental plan; initiation is heavily regulated by transcription factors

Eukaryotic RNA Pol I creates these
rRNA

Eukaryotic RNA Pol II creates these
mRNA

Eukaryotic RNA Pol III creates these
Small RNAs (tRNA, 5S RNA, snRNA, 7S RNA)

Most common Euk promoter sequence
TATA, bound by TFIID

Euk promoters
TATA bound by TFIID, CCAAT bound by CCAAT binding proteins, CpG islands bound by SP1

Enhancers
Distant from +1, upstream or downstream; either orientation works (5-3, 3-5); often found in introns, influence promoter by looping DNA, bound by Enhancer Binding Proteins