65 66 Mayer, B. J., Ren, K., Clark, K. I,. and Baltimore, D. (1993) Cell 73,629-630 Haslarn, K. J., Koide, H. B. and Hemmings, B. A. (1993) Nature (London) 363,309-310 Musacchio, A., Gibson, T., Price, P., Thompson, J. and Saraste, M. (1993) Trends Biochem. Sci. 18, 343-348 Lefkowitz, R. J. (1993) Cell 74,409-412 Bourne, H. K., Sanders, D. A. and McCormick, F. (1991) Nature (London) 349, 117-127 Clark, S. G., Stern, M. J. and Horvitz, R. H. (1992) Nature (London) 356, 340-344 Simon, M. A,, Dodson, G. S. and Rubin, G. M. (1993) Cell 73,169-177 Simon, M. A,, Bowtell, D. L). L., Dodson, G. S., Laverty, T. K. and Rubin. G. M. (1991) Cell 67, 701-716 Bonfini, I,., Karlovich, C. A,, Dasgupta, C. and Banerjee, V. (1992) Science 255,603-606 Bowtell, D., Fu, P., Simon, M. and Senior, P. (1992) Proc. Natl. Acad. Sci. USA. 89, 6.51 1-6515 Egan, S. E., Giddings, B. W., Brooks, M. W., Buday, L., Sizeland, A. M. and Weinberg, K. (1993) Nature (London) 363,4555 1 Buday, I,. and Downward, J. (1993) Cell 73,611-620 I,i, N., Batzer, A,, Daly, R., Skolnik, R., Chardin, P., Bar-Sagi, D., Margolis, B. and Schlessinger, J. (1993) Nature (London) 3 6 3 , 8 5 4 8 67