Targeted random mutagenesis: the use of ambiguously synthesized oligonucleotides to mutagenize sequences immediately 5' of an ATG initiation codon.

The nine base pairs immediately 5' of the initiation codon for the bovine growth hormone (BGH) structural gene have been mutagenized. The mutagenesis method employs the ligation of an ambiguously synthesized oligonucleotide duplex into a previously engineered gap in an expression plasmid for BGH. The mutation method, coupled with hybridization screening, is efficient at isolating 1 and 2 base pair changes within the targeted region. The E. coli cultures harboring the mutant plasmids were assayed for relative levels of BGH expression. The most notable result is the varied effect of substitution of G into the mRNA at various positions in this region.