The homologous terminal sequence of the Streptomyces lividans chromosome and SLP2 plasmid

The chromosome of Streptomyces lividans shares 15.4 kb homology with one en d of the linear plasmid SLP2, consisting of a 10.1 kb terminal sequence fol lowed by the 5.3 kb transposable element Tn4811, The 10.1 kb terminal seque nce was determined. The mean G+C content of this sequence is 67.9 mol% sequ ence was determined. The mean G-C content of this sequence is 67.9 mol% wit h a striking G vs C bias in the last kb, The terminal 232 nt contained 10 p alindromic sequences with potential to form complex secondary structures, O ne typical Streptomyces coding sequence (designated ORF1) of 2643 bp was pr edicted in the determined sequence, The amino acid sequence of the ORF1 pro duct contained a DEAH helicase motif, and exhibited similarity to type I re striction enzyme HsdR subunits in the database, suggesting a possible role in replication of the telomeres. However, all the ORF1 sequences on the chr omosome and SLP2 could be simultaneously knocked out by targeted recombinat ion without affecting the viability of the cells and the linearity of the c hromosome and SLP2. This ruled out ORF1 as an essential component in the ma intenance of the linear chromosome and plasmids.