A Cowdria ruminantium genomic library was constructed in a cosmid vector to serve as a source of
easily accessible and pure C. ruminantium DNA for molecular genetic studies. The cosmid library
contained 846 clones which were arrayed into microtitre plates. Restriction enzyme digestion patterns
indicated that these clones had an average insert size of 35 kb. Probing of the arrays did not
detect any bovine clones and only one of the known C. ruminantium genes, pCS20, was detected.
Due to the high AT content and the fact that C. ruminantium genes are active in the Escherichia coli
host, the C. ruminantium clones were unstable in the SuperCos 1 vector and most clones did not grow
reproducibly. The library was contaminated with E. coli clones and these clones were maintained with
greater fidelity than the C. ruminantium clones, resulting in a skewed representation over time. We
have isolated seven C. ruminantium clones which we were able to serially culture reproducibly; two
of these clones overlap. These clones constitute the first large regions of C. ruminantium DNA to be
cloned and represent almost 10% of the C. ruminantium genome.
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