　Protein molecule is a biopolymer which is composed of 20 kinds of amino acids Each amino acid links with the other one to form a molecule with high molecular weight. Amino acid has a specific side chain; therefore amino acid sequence and steric form of the protein varies from protein to protein. Accordingly, each protein function is different from each other. We have been studying the importance of the protein structure for functioning specifically in the living organisms. We are also going to find out the mechanisms how each protein works properly. Actually, we are orking on two proteins: restriction enzyme HindIII which digests DNA at the specific nucleotide sequence and intermediate filament, a fiber protein which supports the cell internally against external force. For these purposes, we clone the desired gene, determine the nucleotide sequence and express the protein in Escherichia coli in order to analyze its strucutre and biochemical properties. Furhter we are preparing mutant forms of the desired protein and compare them with the wild one.