| Popis: |
Publisher Summary This chapter illustrates that with the recent advent of site-directed mutagenesis, the goal of determining the role of amino acid residues or sequences in the function of a particular protein or enzyme, can be realized. The chapter describes an application of the technique to the lac permease of Escherichia coli. The lac permease is an intrinsic membrane protein, encoded by the lacY gene, that catalyzes symport (cotransport) of β-galactosides with protons. The lacY gene has been cloned and sequenced, and the permease has been purified to homogeneity in a completely functional state. A putative secondary structure model has been proposed based on the circular dichroic spectrum of the purified protein and on the sequential hydropathic character of the amino acid sequence. Although chemical modification of specific amino acid residues in a protein can provide important information, there are drawbacks to this approach. For this reason, oligonucleotide-directed, sitespecific mutageneses to study the structure and function of the lac permease have been utilized. |
