From owner-biophysics@net.bio.net Mon Nov 30 22:00:00 1998 From: "clive delmonte" Newsgroups: bionet.biophysics,bionet.molec-model,bionet.xtallography Subject: DNA Structure: Puzzle Number 1 Date: Tue, 1 Dec 1998 10:01:47 -0000 Lines: 24 X-Newsreader: Microsoft Outlook Express 4.71.1712.3 X-MimeOLE: Produced By Microsoft MimeOLE V4.71.1712.3 NNTP-Posting-Host: 195.7.225.154 Message-ID: <36643bb9.0@news.netdirect.net.uk> X-Trace: 1 Dec 1998 18:55:53 GMT, 195.7.225.154 Path: biosci!agate!newsfeed.berkeley.edu!btnet-peer!btnet!news.netkonect.net!peer.news.nildram.co.uk!news-peer.netdirect.net.uk!news.netdirect.net.uk!195.7.225.154 Xref: biosci bionet.biophysics:4606 bionet.molec-model:2333 bionet.xtallography:4499 In their STM study of nucleic acids (1), Lee et al. recorded in Figure 3(b) lengthy stretches of at least four well-resolved linear DNA duplexes. The vital feature of this image of DNA molecules is that no plectonaemic winding can be discerned. That is, they show no sign of being double-helical. The duplexes consist of long, paired, helices with a consistent, uninterrupted parallel (or antiparallel) contour running between the two strands of each of the four duplexes, whose highlighted features remain exactly in phase with each other over their whole lengths, extending to some 17 - 20 full helical turns. 1 Scanning Tunnelling Microscopy of Nucleic Acids; G. Lee, P.G. Arscott, V.A. Bloomfield & D. Fennell Evans; SCIENCE Vol 244 (1989) 475 - 477 ---------------------------------------------------------------------------- Clive Delmonte .