1. Contribution from Biomolecular Research Unit, Regional Research Laboratory (CSIR), Trivandrum - 695019, India, Central Drug Research Institute, Lucknow 226 001, India, Centre for Cellular and Molecular Biology, Hyderabad 500 007, India, Indian Institute of Chemical Technology, Hyderabad 500 007, India, and Laboratory for the Structure of Matter, Naval Research Laboratory, Washington D.C. 20375