TRANSCRIPTION :

Prokaryote Eukaryote

DNA : Template strand Coding strand

Promoter / TerminatorUpstream / DownstreanStartpoint

Phosphodiester bond formation

- 3’ OH group of the last nt.5’ triphosphate of incoming nt.

RNA chain Pyrophosphate- Reaction rate

in bacteria 4 0 nts. / se

c. At 3 7 ๐C- Translation rate 15 amino a / sec (the same)- DNA replication rate 800 bp. / sec (faster)

Four stages of Transcrip

tion

Template recognitionInitiati

onElongatio

n

Termination

Holoenzyme = initiate transcriptionCore enzyme = synthesize RNASigma factor = recognize specific binding sites

TERMINATION- Intrinsic Terminator- form hairpin in a secondary structure of RNA.- G.C rich region- 7-9 bases of U-run

Rho-dependent terminator:

50-90 basesrich C and poor Gprotein size ~ 46 KD

Rho factor pursues RNA poly. along the RNA and can cause termination

ANTITERMINATIONMechanism in bacterial

phages

Sigma factor

Jacob & Monod (1961): The model for control of gene expression in bacteriaTwo types of seq. in DNA: seq. that code for trans-acting product (usually proteins)cis-acting sequences (usually sites in DNA).A structural gene: any gene that codes for protein (or RNA) productsA recgulator gene: structural gene that codes for a protein involved in regulating the expression of other genes

The lac structural genes in bacteria, lac ZYA

Negative control ; a trans-acting repressor bine to cis-acting operator to turn off transcription.

Positive control; trans-acting factors bind to cis-acting sites in order for RNA polymerase to initiate transcription at the promoter

operator