[19] Isolation of multigene families and determination of homologies by filter hybridization methods

A high proportion of genes in eukaryotes are now known to be members of multigene families. Although initial indications were provided by protein sequencing, the ubiquity of multigene families has been revealed most convincingly by recombinant DNA methods. A list of some of the best-known multigene families, by no means inclusive, would include the genes for histones, globins, immunoglobulins, histocompatibility antigens, actins, tubulins, seed storage proteins, chorion proteins, keratins, collagens, cuticle proteins, yolk proteins, heat shock proteins, and salivary glue proteins. Even genes for proteins that appear homogeneous may belong to multigene families. In the field of hormone research, analysis of gene families related to well-known effectors such as insulin or growth hormone is one of the most exciting areas of current investigation. Many members of multigene families show stage- or tissue-specific expression; a familiar example is the family of globin genes. The study of multigene families is important for understanding the mechanisms of physiological regulation, differential gene expression, and molecular evolution in eukaryotes. A number of filter hybridization methods are used in these studies: phage plaque and bacterial colony hybridization, dot blot hybridization, Southern hybridization, Northern hybridization, and hybrid-selected translation. This chapter focuses on their relatedness and describes how deliberate control of the hybridization stringency maximizes their utility. Examples are cited from studies of the chorion gene families in silkmoths.