Chapter 8 - Major shifts in bacterial transcription. The main contents of this chapter include all of the following: Sigma factor switching, the RNA polymerase encoded in phage T7, infection of E. coli by phage λ,.and another contents. | Molecular Biology Fourth Edition Chapter 8 Major Shifts in Bacterial Transcription Lecture PowerPoint to accompany Robert F. Weaver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sigma Factor Switching Phage infection of bacterium subverts host transcription machinery In process, establishes a time-dependent, or temporal, program of transcription First early phage genes are transcribed This is followed by the later genes Late in the infectious cycle there is no longer transcription of the host genes, only phage genes Change in what genes transcribed is caused by a change in transcription machinery, in RNA polymerase itself 8- Phage Infection Chapter 6 established that s is the key factor in determining specificity of T4 DNA transcription To shift the transcription process s is a likely candidate Study of the process done in B. subtilis and its phage, SPO1 8- Temporal Control of Transcription Like T4, SPO1 has a large genome . | Molecular Biology Fourth Edition Chapter 8 Major Shifts in Bacterial Transcription Lecture PowerPoint to accompany Robert F. Weaver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sigma Factor Switching Phage infection of bacterium subverts host transcription machinery In process, establishes a time-dependent, or temporal, program of transcription First early phage genes are transcribed This is followed by the later genes Late in the infectious cycle there is no longer transcription of the host genes, only phage genes Change in what genes transcribed is caused by a change in transcription machinery, in RNA polymerase itself 8- Phage Infection Chapter 6 established that s is the key factor in determining specificity of T4 DNA transcription To shift the transcription process s is a likely candidate Study of the process done in B. subtilis and its phage, SPO1 8- Temporal Control of Transcription Like T4, SPO1 has a large genome Temporal transcription program: First 5 minutes: expression of early genes During 5 – 10 minutes: expression of middle genes After 10 minutes to end: late genes expressed 8- Transcription Switching This switching is directed by a set of phage-encoded s factors that associate with the host core RNA polymerase These s factors change the host polymerase specificity of promoter recognition from early to middle to late The host s factor is specific for the phage early genes Phage gp28 protein switches the specificity to the middle genes Phage gp33 and gp34 proteins switch to late specificity 8- Sporulation During infection, phage SPO1 changes specificity of host RNA polymerase Same type of mechanism applies to changes in gene expression during sporulation Bacteria can exist indefinitely in vegetative state if nutrients are available Under starvation conditions, B. subtilis forms endospores, tough dormant bodies 8- Sporulation Switching During sporulation, a whole new set of genes .
