1. 1. Richmond, T.J. etal. Nature 311, 532–537 (1984). 2. Richmond, T.J. Nature 326,18–19 (1987). 3. Satchwell, S.C., Drew, H.R. & Travers, A.A. /. molec. Biol. 191, 659–675 (1986). 4. Drew, H.R. & Travers, A.A. /. molec. Biol. 186, 773–790 (1985). 5. Travers, A.A. & Klug, A. Phil. Trans. R. Soc. (in the press). 6. Wu, H–M. & Crothers, D.M. Nature 308,509–513 (1984). 7. Kotlarz, D., Fritsch, A. & Buc, H. EMBOJ. 5, 799–803 (1986). 8. Gronenbom, A.M. etal. J. molec. Biol. 179,751–757 (1984). 9. Liu–Johnson, H.N., Gartenberg, M.R. & Crothers, D.M. Cell 47,995–1005 (1986). 10. Weber, I.T. & Steitz, T.A. Proc. natn. Acad. Sci. U.S.A. 81,3973–3977(1984). 11. Kunke, G., Fritz, H.J. & Ehring, R. EMBOJ. 6, 507–513 (1987). 12. Echols, H. Science 233,1050–1056 (1986). 13. Grindley, N.D.F. etal. Cell32,19–27 (1982). 14. Sherratt, D.J. etal. Cold Spring Harb. Symp. quant. Biol. 59,227–233(1984). 15. Falvey, E. & Grindley, N.D.F. EMBOJ. 6,815–S21 (1987). 16. Drew, H.R., Weeks, J.R. & Travers, A.A. EMBOJ. 4, 1025–1032(1985). 17. McClellan, J.A., Palacek, E. & Lilley, D.M.J. Nucleic Acids Res. 14,9291–9309 (1986). 18. Hatfull, G.F., Noble, S.Z. & Grindley, N.D.F. Cell 49, 103–110(1987). 19. Wasserman, S.A., & Cozzarelli, N.R. Science 232, 951–960(1986). 20. Sadowski, P. /. Bact. 165,341–347 (1986). 21. Better, M. et al. Proc. natn. Acad. Sci U.S.A. 79, 5837–5840(1982). 22. Richet, E., Abcarian, P. & Nash, H.A. Cell46,1011–1021 (1986). 23. Germond, J.E. et al. Proc. natn. Acad. Sci. U.S.A. 72, 1843–1847(1975). 24. Spassky, A., Busby, S. & Buc, H. EM BO J. 3, 43–50 (1984).