HflD, an Escherichia coli protein involved in the lambda lysis-lysogeny switch, impairs transcription activation by lambdaCII

• Published in: Archives of biochemistry and biophysics 2010-01, Vol.493 (2), p.175-183
• Main Authors: Parua, Pabitra K, Mondal, Avisek, Parrack, Pradeep
• Format: Article
• Language: English
• Subjects: Bacteriophage lambda - physiology; DNA, Viral - genetics; DNA, Viral - metabolism; Escherichia coli - genetics; Escherichia coli - metabolism; Escherichia coli - virology; Escherichia coli Proteins - genetics; Escherichia coli Proteins - metabolism; Lysogeny - physiology; Membrane Proteins - genetics; Membrane Proteins - metabolism; Models, Biological; Multiprotein Complexes - genetics; Multiprotein Complexes - metabolism; Peptides - genetics; Peptides - metabolism; Promoter Regions, Genetic - physiology; Transcription Factors; Viral Proteins
• ISSN: 1096-0384
• DOI: 10.1016/j.abb.2009.10.010

The CII protein of bacteriophage lambda is the key regulator for the lytic-lysogenic choice of the viral lifecycle. An unstable homotetrameric transcription activator of the three phage promoters p(E), p(I) and p(aQ), lambdaCII is stabilized by lambdaCIII and destabilized by the host protease, Escherichia coli HflB (FtsH). In addition, other E. coli proteins HflK, HflC and HflD also influence lysogeny by acting upon CII. Among these, HflD (22.9kDa), a peripheral membrane protein that is exposed towards the cytoplasm, interacts with CII and decreases the frequency of lysogenization of lambda by stimulating the degradation of CII. In this study, we show that in addition to helping CII degradation, HflD inhibits the DNA binding by CII, thereby inhibiting CII-dependent transcription activation. From biochemical, biophysical and modelling studies we also suggest that HflD-CII interaction takes place through the Cys31-accessible surface area of monomeric HflD, which binds to tetrameric CII as a 1:1 complex.