| 摘要 |
In the present invention, there is disclosed 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 FIGURE 1 (SEQ ID NO: 1), or a degenerate variant thereof, but which nucleotide sequence further comprises one or more mutations encoding an amino acid substitution at one or more amino acid residues corresponding to amino acid position 38, 48, 89,99,111,136,154,179,228,238,289, or 298 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 avermectins that is different from the ratio produced by cells of S. avermitilis strain ATCC 53692 that instead express only the wild-type aveC allele. There is also disclosed a vector containing the above-described polynucleotide molecule and a host cell, preferably Streptomyces, particularly S. avermitilis, containing this polynucleotide molecule or a recombinant vector thereof. Further disclosed is a process for preparing the S. avermitilis strain by a corresponding mutation of the S. avermitilis strain cells. |
