Patent ID: 7388085

Claim:
An isolated polynucleotide molecule comprising a nucleotide sequence that is otherwise the same as the Streptomyces avermitilis aveC allele, the S. avermitilis AveC gene product-encoding sequence of plasmid pSE186 (ATCC 209604) or the nucleotide sequence of the AveC ORF of S. avermitilis as presented in FIG. 1 (SEQ ID NO:1), or a degenerate variant thereof, which nucleotide encodes a functionally equivalent aveC gene product and which nucleotide sequence further comprises mutations encoding one or more amino acid substitutions in the amino acid sequence of SEQ ID NO:2, such that cells of S. avermitilis strain ATCC 53692 in which the wild-type aveC allele has been inactivated and that express the polynucleotide molecule comprising the mutated nucleotide sequence produce a class 2:1 ratio of avermetins that is reduced compared to the ratio produced by cells of S. avermitilis strain ATCC 53692 that instead express only the wild-type aveC allele, wherein when the class 2:1 avermectins are cyclohexyl B2: cyclohexyl B1 avermectins the ratio of class 2:1 avermectins is 0.35:1 of less, wherein the combinations of amino acid substitutions comprise substitutions at both D48 and G179.