Amplification of the isopenicillin N synthetase gene in a strain of Penicillium chrysogenum producing high levels of penicillin

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Abstract
Summary The isopenicillin N synthetase (IPNS) gene has been isolated from wild-type Penicillium chrysogenum and used as a probe to detect the equivalent gene on Southern blots of genomic DNA from a mutant producing high levels of penicillin. The IPNS gene in this strain is contained within a region of DNA of wild-type restriction pattern that extends for at least 39 kb and is present at between 8 and 16 copies. The steady state level of IPNS mRNA in the mutant producing high levels of penicillin is between 32-and 64-fold of that of the wild type, suggesting that the rate of transcription of some or all of the copies has been increased. In addition we have also shown that both the IPNS mRNA and enzyme is present throughout the growth phase in both strains under the culture conditions used. IPNS enzyme activity is greatly increased in the strain with the high penicillin titre.