ConclusionFaced with these possibilities, what should we, as scientists, do? We are in some sense a privileged minority group, and all of us should be ready to exercise the grave responsibility which we all share, "to increase public understanding and appreciation of the importance and promise of the methods of science in human progress." These words are quoted from a statement of the objectives of this Association. A second objective of our organization is "to improve the effectiveness of science in the promotion of human welfare." These two should be the articles of our scientific creed in the years ahead. Furthermore, as scientists we should not ConclusionFaced with these possibilities, what should we, as scientists, do? We are in some sense a privileged minority group, and all of us should be ready to exercise the grave responsibility which we all share, "to increase public understanding and appreciation of the importance and promise of the methods of science in human progress." These words are quoted from a statement of the objectives of this Association. A second objective of our organization is "to improve the effectiveness of science in the promotion of human welfare." These two should be the articles of our scientific creed in the years ahead. Furthermore, as scientists we should not lose our perspective but should recall the history of science and remember that it has survived pestilence, wars, and disaster and has surmounted barriers of race, religion, and language. Beyond this, it is even more important to recall, in a gray period of international tension, that all members of the human race, throughout its evolution and long history, have had a common opponent. This is inscrutable nature with her seemingly inexorable laws, her hosts of organisms and parasites, her hurricanes and catastrophic events of all kinds. For our human race the central problem is still that of understanding nature and attempting to control it. Here the thinking and tools of modern science have a great contribu-Dr. Steward is professor of botany and director of the Laboratory of Cell Physiology, Growth, and Development at

The proteasome is a large multicatalytic proteinase that plays a role in the generation of peptides for presentation by major histocompatibility complex class I molecules. The 20S proteolytic core of mammalian proteasomes is assembled from a group of 17 protein subunits that generate a distinctive pattern of spots upon two-dimensional gel electrophoresis. The genes for most of these subunits have been cloned from humans and rats. We isolated cDNA clones for the mouse orthologues of ten of the subunits [PSMA1 (C2), PSMA2 (C3), PSMA3 (C8), PSMA4 (C9), PSMA5 (ZETA), PSMA6 (IOTA), PSMA7 (C6-I), PSMB2 (C7-I), PSMB3 (C10-II), and PSMB5 (X)] to complete the cloning of all of the mouse subunits. Using antisera raised against these subunits or their orthologues, we verified the identity of these proteins by two-dimensional NEPHGE-PAGE.

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