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and realized with my colleagues at Eiitvds Lorand University,Budapest, is based on the Nobel Prize-winning “solidphase procedure” of R.B. Merrifield [11.According to his method, the first amino acid is attached to a solid support (tiny polymer beads, about 10million in 1gram), then further amino acids are coupled sequentially to it, and finally, the peptide is cleavedfrom the support. In my method [2], the following three simple operations are repeatedly used: 1.The solid support is divided into 20 equal portions 2. A different amino acid is coupled to each portion 3. The portions are mixed. These operations are repeated until the desired length of a peptide chain is achieved. The procedure is demonstrated in a simplified form in Fig. 2. If the 20 natural amino acids are used in five consecutive cycles of the above three operations, all the possible 3.2 million pentapeptides are formed in nearly equal molar quantities. We carried out this synthesismanually, without the help of today’sautomatic synthesizers,and still were able to finish it in 5 days. Although the end product is a mixture of peptides, good methods are availablefor identification of the biologically important component. My method, along with a few others, brought about radical improvements in the efficiencyof pharmaceutical research and established a fastkrowing new branch of science: combinatorial chemistry. References 1. R.B. Merrifield,‘Solid Phase Peptide Synthesis. I. The Synthesisof a Tetrapeptide,”Journaloffhe Am’canChemicalSociety85,2149-2154(1963). 2. A. Furka, F. SebestyCn,M. Asgedom and G. Dib6, ”Cornucopiaof Peptides by Synthesis,”in Absfractso f the 14fhInfernafionalCongresso f Biochmistry , Prague,Czechoslovakia5 (1988) p. 47. UNRAVELINGTHE MYSTERIES OF FLOWER DEVELOPMENT Elliot Meyerowitz,Division of Biology 156-29, California Institute of Technology , Pasadena, CA 91125, U.S.A. E-mail: . The work reported in this Abstract was awarded the 1996LVMH Science for Art Prize. I am a biologist; my colleagues and I use the methods of genetic analysisand molecuiar biology to try to understand how a complex living organism develops from a fertilized egg. A fertilized egg is a single cell, while a mature plant or animal contains many millions of cells of different types. During development, the single egg cell divides, and its descendants divide, to provide huge numbers of cells in mature form. Somehow,each of the cells that forms must learn its position in the organism-either by receiving some type of positional cues from its neighbors or by having some global positional coordinates. The cells must know their positions because they eventuallyform specialized cell types with a specificposition in the mature organism. For example , cornea cells form only in eyes, indeed, only in specificparts of eyes. We would like to know how each cell learns its position and then acts on its positional knowledge to form the appropriate cell type. We use flowers to solve this problem, because plant development is in many ways simpler than animal development , and because flowers are so highly (and attractively) organized in their patterns of organ numbers, organ positions and organ types. We knew before starting our work that there are genes (genesare each a few thousand base pairs of deoxyribonucleic acid [DNA],and each contains information for the construction of a single type of protein) that represent critical instructions for pattern formation in flowers. Over more than a millennium , flower breeders (the records go back to ninth-centuryChina) have purposely collected genetic variants that have altered floral patterns. Most of our cultivated flowers are descendants of such mutants-for example, double flowerssuch as ‘Pink Perfection ’ camellias, which have petals in place of their male and female sex organs . We have reproduced the genetic work of our ancestors, choosing a small plant well-suited for laboratory work because it grows rapidly and requires little space-a member of the mustard family named Arabidopsis thaliana. By using mutagenic treatments, we have made many mutant lines that have normal floral organs in inappropriate places, such as petals in the positions usually occupied by stamens, or carpels (fruit parts) in the positions usually filled by sepals. Each mutation represents the loss of action of a gene whose protein product plays a role in informing cells of their positions; when the gene...


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