Department of Biochemistry, Bose Institute, P 1/12, C.I.T. Scheme VIIM, Kolkata-700054, India.
Abstracts of the papers presented at the International Conference of Indian Virological Society on “Emerging and Re-emerging viral Diseases of the Tropics and Subtropics” at Indian Agricultural Research Institute, New Delhi, India, December 11–14, 2007.
The temperate coliphage lambda has to decide between the lytic and the lysogenic pathways of development. This decision depends upon factors such as temperature, presence of nutrients and multiplicity of infection. Crucial to this decision is the viral protein CII, an unstable transcription activator. The virus senses the growth conditions of the bacterium through a host-phage crosstalk that serves to alter CII stability. When CII is stabilized, E. coli follows the lysogenic pathway; destabilization of CII leads to cell lysis. Chiefly from genetic studies, a number of proteins from lambda (CIII) as well as from E. coli (HflB, HflX, HflK, HflC and HflD) have been implicated in influencing the lysis-lysogeny decision, through their effects on CII. Apart from HflB, an ATP-dependent metalloprotease that processively degrades CII, none of the other proteins have been studied at the structural level. With a view to understand the functions of these proteins (with respect to the lysis-lysogeny decision) at the molecular level, CII, CIII, HflX, HflK, HflC and HflD protein were purified. The structure of CII was studied by various biochemical and biophysical methods including X-ray crystallography, leading to an explanation of its recognition of direct repeat sequences in DNA. CIII was found to be a dimer having a central helical region that inhibits the proteolytic activity of HflB by binding to the enzyme. Various protein-protein interactions between these proteins were examined by GST/Ni-NTA pulldown and other methods. From these studies, some clues to the activities of these proteins have emerged.
