Exon shuffling: New genes from old

Abstract

Introduction Over the past several years, scientists in- volved in the study of the immune response have witnessed a minor revolution as the techniques of molecular biology have been applied to some of the genes of the immune system. In particular, the genes that encode the major histocompatibility antigens, both the class-I (H-2, Qa, and Tla in the mouse; HLA-A, HLA-B, and HLA-C in man) and the class-II (I-A and I-E in the mouse; HLA- DP, HLA-DQ, and HLA-DR in man) have been cloned, representative genes have been sequenced, and the isolated DNA sequences have been introduced into tissue culture cells in the first steps of the detailed analysis of their expression [ 1 ]. One of the most exciting aspects of a mo- lecular biological approach to the study of the immune system has been the opportunity to generate novel immunologically active genes by in vitro mutagenesis, and to analyze their function following their introduction into tis- sue culture cells. Thus, either major deletions or rearrangements ofexons (resulting in gross changes in the domain organization of the encoded protein [2-1 I]) or point mutations (leading to specific amino acid substitutions [12]) can be generated at will. The contribu- tion of particular regions of the expressed cell surface antigen to either serological or cell- mediated recognition can be evaluated. The first such in vitro mutagenesis experiments (now commonly referred to as exon-shuffiing experiments) were of the type involving ma- jor rearrangements of exons derived from different murine class-I genes [2]. Since these kinds of studies have been performed' in sev- eral different laboratories with a general con- sistency to the results and interpretations, we will focus our attention in this brief review on them. More recently, similar kinds of experi- ments have been performed in the human class-I system [9] and in the murine class-II system [10]. In addition, in our own labora- tory, class-II/class-I recombinant genes have been generated and analyzed [ 11 ].