A new high-capacity cosmid vector and its use.

The construction of a cosmid, MUA-3, designed for the convenient cloning of eukaryotic DNA segments up to 48 kb in length is described. The cosmid contains all of the plasmid pBR322 with approx. 400 bases of lambda DNA, including the cohesive end site, inserted at the pBR322 PstI endonuclease recognition site. Methods for using this vector to construct several types of Drosophila melanogaster genomic DNA libraries are given, and libraries made by these methods are characterized. A sheared Drosophila DNA-EcoRI linker library is shown to stably maintain average Drosophila DNA inserts of over 40 kb and up to 48 kb, and the efficiency of producing clones by a partial restriction and ligation method is shown to be over 3 X 10(5) clones/microgram of Drosophila DNA.