A Biological Unified Field Theory

assembled into complexes. These reactions include acetylation and deacetylation of histones, chromosome remodeling, etc. The authors are, of course, aware of Genes & Signals this, and have broadened their use of the word " recruit-By Mark Ptashne and Alexander Gann ment " to include, for example, the role of the lambda Cold Spring Harbor, NY: Cold Spring Harbor CI repressor in stimulating transcription at the phage Laboratory Press (2001). 208 pp. $59.00 Prm promoter. RNA polymerase binds readily to Prm, but fails to form an open complex (melt the DNA). Increasing the local concentration of RNA polymerase Recall the days of yesteryear when, for biologists, en-does not activate Prm. However, CI bound at a nearby zymes were enzymes and didn't need any help in finding site allows open complex formation. It drives the reac-their substrates. Alas, those simple times are long gone. tion toward the productive complex, presumably by sta-Instead we are faced with the horrible realization that bilizing an intermediate in its formation. The interacting proteins rarely see their ligands without being led by faces of CI and RNA polymerase are known, thanks to the nose to them. So, for example, RNA polymerase earlier work by Ptashne, but the fine molecular details once promptly landed on a promoter and revved up to of the reaction are not. Is this recruitment? transcribe a gene. It turns out, in fact, that for most But why all this pilpul over a single word! Let's forget promoters, RNA polymerase requires additional pro-about it and move onto the meat of the book itself. teins just to find the site. And other proteins interfere with Ptashne and Gann have written a clear and intelligent its attachment. The number of such auxiliary factors, distillation of the various assembly pathways, especially especially in eukaryotes, is mind boggling, and they are in transcription initiation. all tagged with impossible-to-decipher acronyms— The authors start with the simplest systems, phage usually several for the same factor. The situation is and bacteria, and work toward the more complex. They scarcely better in signal transduction. A hormone can describe three types of activator-dependent transcrip-only relay its message to the nucleus via passage tion initiation in bacteria. In one, the activator and RNA through a long series of proteins, most of which have polymerase bind weakly near the promoter, but their to be spatially constrained to transmit the signal. Even cooperative interaction stabilizes the …