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A basic/hydrophobic cleft of the T4 activator MotA interacts with the C‐terminus of E. coli σ 70 to activate middle gene transcription
Author(s) -
Bonocora Richard P.,
Caignan Gregori,
Woodrell Christopher,
Werner Milton H.,
Hinton Deborah M.
Publication year - 2008
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2008.06276.x
Subject(s) - biology , activator (genetics) , transcription (linguistics) , gene , transcription factor , microbiology and biotechnology , genetics , linguistics , philosophy
Summary Transcriptional activation often employs a direct interaction between an activator and RNA polymerase. For activation of its middle genes, bacteriophage T4 appropriates Escherichia coli RNA polymerase through the action of two phage‐encoded proteins, MotA and AsiA. Alone, AsiA inhibits transcription from a large class of host promoters by structurally remodelling region 4 of σ 70 , the primary specificity subunit of E. coli RNA polymerase. MotA interacts both with σ 70 region 4 and with a DNA element present in T4 middle promoters. AsiA‐induced remodelling is proposed to make the far C‐terminus of σ 70 region 4 accessible for MotA binding. Here, NMR chemical shift analysis indicates that MotA uses a ‘basic/hydrophobic’ cleft to interact with the C‐terminus of AsiA‐remodelled σ 70 , but MotA does not interact with AsiA itself. Mutations within this cleft, at residues K3, K28 and Q76, both impair the interaction of MotA with σ 70 region 4 and MotA‐dependent activation. Furthermore, mutations at these residues greatly decrease phage viability. Most previously described activators that target σ 70 directly use acidic residues to engage a basic surface of region 4. Our work supports accumulated evidence indicating that ‘σ appropriation’ by MotA and AsiA uses a fundamentally different mechanism to activate transcription.