In In Vitro Mutagenesis Protocols leading experts from industrial and academic laboratories describe easily reproducible procedures for site-directed and random mutagenesis. Site-directed protocols include those based on strand-selection, PCR (including "splicing by overlap extension" and the "megaprimer" procedure), the ligase chain reaction, positive antibiotic selection, unique restriction site elimination, gapped heteroduplex formation, and solid-phase capture with the biotin/ strepavidin system. Many techniques can be used with virtually any double-stranded DNA plasmid. The random mutagenesis protocols include methods based on PCR, degenerate oligonucleotides, cassette mutagenesis, nested deletion mutagenesis, and a specialized E. coli mutator strain. These invaluable protocols facilitate the study of gene regulation and structure/function relationships in proteins and permit modification of DNA sequences for purposes such as vector construction.