Conceptos Basicos En Homeostasis

beled at the 5' end were purified by Sephadex G50 chromatography in a 0.3M sodium acetate, 0.OlM tris-HCI, pH 7.9, 0.001M EDTA system, and concentrated by precipitation with ethanol. 6. A. Maxam and W. Gilbert, Proc. Natl. Acad. Sci. U.S.A. 74, 560 (1977). 7. Low molecular weight DNA fragments were resolved by electrophoresis at < 10 volt/cm in gels containing 10 percent polyacrylamide(acrylamide: N,N'-methylenebisacrylamide = 25: 1) in one-half strength TBE [0.05M tris-borate, pH 8.3, 0.001M EDTA, A. Peacock and C. Dingman, Biochemistry 7, 668 (1968)] with 25 percent glycerol. Glycerol improves band sharpness dramatically. 8. J. Dahlberg and F. Blattner, in Virus Research, C. Fox and W. Robinson, Eds. (Academic Press, New York, 1973), p. 533. 9. M. Rosenberg, personal communication. 10.D. Kleid, Z. Humayun, A. Jeffrey, M. Ptashne, Proc. Natl. Acad. Sci. U.S.A. 73, 293 (1976). 11. M. Rosenberg, B. de Crombrugghe, R. Musso, ibid., p. 717. 12. G. Scherer, G. Hobom, H. Kossel, Nature (London) 256, 117 (1977). 13. V. Pirotta, personal communication. 14. E. Schwarz, G. Scherer, G. Hobom, H. K6ssel, personal communication. 14a.G. Scherer, G. Hobom, H. Kossel, personal communication.15. B. Westmoreland, W. Szybalski, H. Ris, Science 163, 1343 (1969). 16. D. Hewish, K. Smith, J. Spencer, Virology 74, 363 (1976). 17. A. Rambach, ibid. 54, 270 (1973). 18. W. Dove, H. Inokuchi, W. Stevens, in The Bacteriophage Lambda, A. D. Hershey, Ed. (Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y., 1971), p. 747. 19. W. Szybalski et al., J. Cell. Physiol. 74 (Suppl. 1), 33 (1969). 20.H. Inokuchi, W. Dove, D. Freifelder, J. Mol. Biol. 74, 721 (1973). 21. N. Kleckner, Virology 79, 174 (1977). 22. M. Schnos and R. Inman, J. Mol. Biol. 55, 31 (1971); A. Kozinski and B. Lindqvist, personal communication. 23. The X ori region, defined by the ori- mutations, has two dPy dPu stretches (18 bp and 18 of 21 bp) in which the pyrimidines are on the r strand. The origin of Col Elreplication, defined by the site at which deoxyribonucleotides are added onto an RNA primer in vitro, is 20 bp away from a dPy dPu stretch (21 of 24 bp) with purines on the transcribed strand [J.-I. Tomizawa, H. Ohmori, R. Bird, Proc. Natl. Acad. Sci. U.S.A. 74, 1865 (1976)]. The origin region for phage fd DNA replication, defined by an in virto RNA primer, contains a dPy * dPu stretch (29 of 32 bp) withpyrimidines on the transcribed strand (C. Gray, R. Sommer, C. Polke, E. Beck, H. Schaller, personal communication). The pyrimidine tract CTC5 lies in the region of the A gene dependent gap in OX174 at the start of RF to RF replication [S. Eisenberg, B. Harbers, C. Hours, D. Denhardt, J. Mol. Biol. 99, 197 (1975)]. 24. F. Sanger, G. Air, B. Barrell, N. Brown, A. Coulson, J. Fiddes, C. Hutchison, P.Slocombe, M. Smith, Nature (London) 265, 687 (1977); P. Baas, H. Jansz, R. Sinsheimer, J. Mol. Biol. 102, 633 (1976); S. Eisenberg, B. Harbers, C. liours, D. Denhardt, ibid. 99, 197 (1975). 25. R. Fisher, The Genetical Theory of Natural Selection (Clarendon, Oxford, 1930). 26. We believe that the deletions observed in the nucleotide sequences for r93, r99, and r96 correspond to the orti lesions.The ori- mutants were isolated without mutagenesis and occur with frequencies inconsistent with multiple mutations. The deletions could not have arisen during cloning, because they are present in the ori- phages ANam7NamS3cI8S7r93 and ANam7NarnS3c1857r99. The 0 protein made from the DNA of these phages in vitro is smaller than that made from DNA of the oril parent phage when measured by SDSpolyacrylamide gel electrophoresis (J. Yates and M. Furth, unpublished results, using techniques described in J. Yates, W. Gette, M. Furth, M. Nomura, Proc. Natl. Acad. Sci. U.S.A. 74, 689 (1977)]. The size of each deletion is consistent with the changes in molecular weights of the 0 protein made in vitro and of DNA restriction fragments. Finally, the recombinational map of the ori- mutations is...