Characterization of a plasmid replicative origin from an extreme thermophile

The minimal replicative origin from a 16-kbp natural plasmid of Thermus sp. ATCC 27737 is described. The 1798-bp sequence encodes a single protein (RepA) whose expression is required for replication. This requirement is extended to 200 bp upstream the coding region, which contains promoter-like sequences transcriptionally active in E. coli. Despite the absence of typical iterons, we show that an N-terminal fragment of this protein binds to a DNA fragment internal to its own coding sequence. As this DNA fragment contains an unusually A+T rich sequence surrounded by C+G rich stretches, the possible location of the replicative origin within the region encoding RepA is proposed. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.