BIOL 367- Midterm Exam Guide - Comprehensive Notes for the exam ( 87 pages long!)
Document Summary
Chapter 8 major shifts in bacterial transcription. The earliest genes are transcribed by the host holoenzyme. When the phage first infects the cell, the host holoenzyme is therefore the only rna polymerase still available. The b. su(cid:271)tilis (cid:272)o(cid:396)e (cid:272)o(cid:374)sist of t(cid:449)o la(cid:396)ge a(cid:374)d ", a(cid:374)d t(cid:449)o s(cid:373)all , a(cid:374)d o(cid:374)e (cid:448)e(cid:396)y s(cid:373)all . The holoenzyme also has a it helps to prevent binding to non-promoter regions. Gp28 is a novel sigma factor that accomplishes t(cid:449)o thi(cid:374)gs: it di(cid:448)e(cid:396)ts the host"s poly(cid:373)erase from transcribing host genes, and it switches from early to middle phage transcription. Gp33 and gp34, the products of two phage middle genes (genes 33 and 34). These proteins constitute a sigma factor that can replace gp28and direct the altered polymerase to transcribe the phage late genes in preference to the middle genes. The core polymerase apparently has a versatile sigma binding site. Genetic studies have shown that mutations in gene 28 prevent the early-to-middle switch.
