Gene regulation Biology, 5 October 2010 Donald Winslow Operons in prokaryotes

Gene regulation in prokaryotes References: Griffiths et al., 9th ed., Ch. 10, pp Hoefnagels, Biology, 1 st ed., Ch. Pp Klug et al., Concepts of Genetics, 9th ed., Ch. 17 pp , ,

Regulatory proteins & binding sites on DNA Regulatory proteins Domains Allosteric site Binds to allosteric effector Presence of effector reflects conditions in cell DNA-binding domains binds to binding site on DNA Sometimes other sites bind to other regulatory proteins Binding sites on DNA Promoter is recognized by RNA polymerase

Prokaryotic gene regulation Switch operon on or off in response to stimuli Positive regulation Activator binds to activator-binding site Negative regulation Repressor binds to operator prevents transcription

Lactose metabolism in E. coli Repressor gene is transcribed to produce repressor protein. When lactose is absent, repressor protein binds to operator and prevents transcription of structural lactose-metabolism genes. When lactose is present, lactose binds to repressor protein and changes its shape so it can no longer bind to operator. Transcription of structural lactose-metabolism genes is blocked.

Catabolite repression