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J Bacteriol, May 1998, p. 2468-2474, Vol. 180, No. 9
Max-Volmer-Institut,
Received 4 December 1997/Accepted 11 February 1998
The actinomycin synthetases ACMS I, II, and III catalyze the
assembly of the acyl peptide lactone precursor of actinomycin by a
nonribosomal mechanism. We have cloned the genes of ACMS I
(acmA) and ACMS II (acmB) by hybridization
screening of a cosmid library of Streptomyces chrysomallus
DNA with synthetic oligonucleotides derived from peptide sequences of
the two enzymes. Their genes were found to be closely linked and are
arranged in opposite orientations. Hybridization mapping and partial
sequence analyses indicate that the gene of an additional peptide
synthetase, most likely the gene of ACMS III (acmC), is
located immediately downstream of acmB in the same
orientation. The protein sequence of ACMS II, deduced from
acmB, shows that the enzyme contains two amino acid activation domains, which are characteristic of peptide synthetases, and an additional epimerization domain. Heterologous expression of
acmB from the mel promoter of plasmid PIJ702 in
Streptomyces lividans yielded a functional 280-kDa peptide
synthetase which activates threonine and valine as enzyme-bound
thioesters. It also catalyzes the dipeptide formation of
threonyl-L-valine, which is epimerized to
threonyl-D-valine. Both of these dipeptides are enzyme
bound as thioesters. This catalytic activity is identical to the in
vitro activity of ACMS II from S. chrysomallus.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Molecular Cloning of the Actinomycin Synthetase
Gene Cluster from Streptomyces chrysomallus and Functional
Heterologous Expression of the Gene Encoding Actinomycin
Synthetase II
*
Corresponding author. Mailing address:
Max-Volmer-Institut, Fachgebiet Biochemie und Molekulare Biologie,
Technische Universität Berlin, Franklinstrasse 29, D-10587
Berlin-Charlottenburg, Germany. Phone and fax: 49 30 314 73522. E-mail:
Ullrich{at}chem.TU-Berlin.de.
J Bacteriol, May 1998, p. 2468-2474, Vol. 180, No. 9
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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