1. Dr. B. C. Guha Centre for Genetic Engineering and Biotechnology, Department of Biochemistry, University College of Science, University of Calcutta, 35 Ballygunge Circular Road, Calcutta 700 019, India, Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560 012, India, and Department of Biophysics, Bose Institute, P 1/12 CIT Scheme VII M, Calcutta 700 054, India