title: Role of C-terminal residues in oligomerization and stability of lambda CII: implications for lysis-lysogeny decision of the phage.
abstract: A crucial element in the lysis-lysogeny decision of the temperate coliphage lambda is the phage protein CII, which has several interesting properties. It promotes lysogeny through activation of three phage promoters p(E), p(I) and p(aQ), recognizing a direct repeat sequence TTGCN6TTGC at each. The three-dimensional structure of CII, a homo-tetramer of 97 residue subunits, is unknown. It is an unstable protein in vivo, being rapidly degraded by the host protease HflB (FtsH). This instability is essential for the function of CII in the lysis-lysogeny switch. From NMR and limited proteolysis we show that about 15 C-terminal residues of CII are highly flexible, and may act as a target for proteolysis in vivo. From in vitro transcription, isothermal calorimetry and gel chromatography of CII (1-97) and its truncated fragments CIIA (4-81/82) and CIIB (4-69), we find that residues 70-81/82 are essential for (a) tetramer formation, (b) operator binding and (c) transcription activation. Presumably, tetramerization is necessary for the latter functions. Based on these results, we propose a model for CII structure, in which protein-protein contacts for dimer and tetramer formation are different. The implications of tetrameric organization, essential for CII activity, on the recognition of the direct repeat sequence is discussed.
authors.affiliation: Department of Biochemistry, Bose Institute, P 1/12, CIT Scheme VIIM, Kolkata 700 054, India.
authors.forename: Ajit Bikram
authors.initials: AB
authors.lastname: Datta
authors.forename: Siddhartha
authors.initials: S
authors.lastname: Roy
authors.forename: Pradeep
authors.initials: P
authors.lastname: Parrack
mesh_terms: D000595:Amino Acid Sequence; D010582:Bacteriophage lambda / Q000378:metabolism; D001665:Binding Sites; D002151:Calorimetry; D002845:Chromatography; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli; D008242:Lysogeny; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013997:Time Factors; D014157:Transcription Factors / Q000737:chemistry*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014357:Trypsin / Q000494:pharmacology; D014764:Viral Proteins
chemical_list: D014157:Transcription Factors; D014764:Viral Proteins; C039000:cII protein, bacteriophage lambda; D014357:Trypsin