AUD4, a new amplifiable element from Streptomyces lividans.

After transformation of the Streptomyces lividans chloramphenicol-sensitive, arginine-auxotrophic mutant strain AJ100 with a derivative of plasmid SCP2, some of the regenerated protoplasts contained an 8.2 kb DNA sequence amplified to several hundred copies per chromosome. The corresponding non-amplified sequence, called AUD4, was isolated from a lambda phage genomic library of S. lividans 1326. Two cytosine residues were the only directly repeated nucleotides at the ends of the element, indicating that AUD4 is a class I amplifiable sequence. The element mapped in the AseI-D fragment of the S. lividans chromosome, where other class I amplifications have been described. The complete element was sequenced and 10 ORFs were identified. Some of the deduced proteins are highly conserved in other organisms but a putative function could be attributed to only a few of them. Duplication of AUD4 by integration of an Escherichia coli plasmid carrying various parts of AUD4 and a thiostrepton-resistance gene in S. lividans AJ100, ZX7 or TK64 induced amplification of the integrated plasmid, AUD4 or both at high frequency.