Chapter 8 - Major shifts in bacterial transcription. In this chapter, students will be able to understand: Sigma factor switching, the RNA polymerase encoded in phage T7, infection of E. coli by phage λ,.and another contents. | Molecular Biology Fifth 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. Major Shifts in Bacterial Transcription Bacteria control the transcription of a very limited number of genes at a time through the use of operons More radical shifts in gene expression require more fundamental changes in the transcription machinery Three major mechanisms: -factor switching RNA polymerase switching antitermination 8- 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 the genes that are transcribed is caused by a change in transcription . | Molecular Biology Fifth 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. Major Shifts in Bacterial Transcription Bacteria control the transcription of a very limited number of genes at a time through the use of operons More radical shifts in gene expression require more fundamental changes in the transcription machinery Three major mechanisms: -factor switching RNA polymerase switching antitermination 8- 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 the genes that are transcribed is caused by a change in transcription machinery, in RNA polymerase itself 8- Phage Infection 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 Like T4, SPO1 has a large genome SPO1 has a temporal program of transcription 8- Temporal Control of Transcription in SPO1 Temporal transcription program: First 5 minutes: expression of early genes After 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 the specificity to late genes 8- Sporulation .
