Genetic Instability and Genome Structure in Streptomyces

J. Cullum, M. Redenbach, Annette Arnold, U. Rauland, S. Kerbeck, H. Sutter

LB Genetik, Universität Kaiserslautern, Postfach 3049, D-67663 Kaiserslautern, F. R. G.

Article history:
Received June 23, 1994 
Accepted September 26, 1994

Summary:
Streptomyces lividans 66 is used as a model strain to study the mechanisms of genetic instability in Streptomyces. Tlic instability involves deletion of up to about 1 Mb of the 8 Mb genome and often amplification of neighbouring sequences. Recent work showed that the chromosome of S. lividans is linear and the deletogenic regions were localized to the two ends of the chromosome. A closer study of deletion mutants showed that some deletions had only one end of the chromosome and that one end was replaced by a tandem amplification of chromosomal sequences with deletion of the ca. 300 kb of DNA between the end and the amplification, in contrast deletions affecting the other end resulted in loss of both chromosomal ends and circularization of the chromosome. The reasons for this asymmetry between the chromosome ends will be discussed. Artificial duplications in the chromosome in an amplifiable region can stimulate amplification both of the duplicated sequence and of another amplifiable region about 7 Mb away on the linear chromosome.