Cosmids: a type of plasmid gene-cloning vector that is packageable in vitro in bacteriophage lambda heads.

Abstract

Evidence is presented that ColEl hybrid plasmids carrying the cohesive-end site (cos) of .lambda. can be used as gene cloning vectors in conjunction with the .lambda. in vitro packaging system of Hohn and Murray. Due to the requirement for a large DNA molecule for efficient packaging, there is a direct selection for hybrids carrying large sections of foreign DNA. The small vector plasmids do not contribute a large background in the transduced population [Escherichia coli] which is therefore markedly enriched for large hybrid plasmids (over 90%). The efficiency of the in vitro packaging system is on the order of 105 hybrid clones/microgram of foreign DNA for hybrids in the 20-30 million dalton range.