  In nature the three-dimensional structure of a protein is encoded in the
corresponding gene. In this paper we describe a new method for encoding the
three-dimensional structure of a protein into a binary sequence. The feature of
the method is the correspondence between protein-folding and ``integration''. A
protein is approximated by a folded tetrahedron sequence. And the binary code
of a protein is obtained as the ``second derivative'' of the shape of the
folded tetrahedron sequence. With this method at hand, we can extract static
structural information of a protein from its gene. And we can describe the
distribution of three-dimensional structures of proteins without any subjective
hierarchical classification.
