With eukaryotes, attempts to clone segments of DNA using recombinant DNA technology from warm-blooded vertebrates genomes were to be performed only with vector-host systems that had demonstrably restricted growth capabilities outside the laboratory and in a moderate risk containment facility. This was because they potentially contained cryptic viral genomes that were potentially pathogenic to humans. However, unless the organism made a dangerous product, recombinant DNAs from cold-blooded vertebrates and all other lower eukaryotes could be constructed and propagated with the safest vector-host system available in low risk containment facilities. Additionally, purified DNA from any source that performed known functions and was judged to be non-toxic could be cloned with available vectors in low risk containment facilities.