摘要:
A vector according to the invention with a positive selection possibility for cloning a DNA sequence into a host cell transformed with the vector, wherein the vector contains suitable restriction cleavage sites within a selection gene the functional expression of which is prevented by insertion of the foreign gene is characterized in that it contains a modified cap gene as the selection gene which codes for a CAP protein with modified DNA binding specificity the expression of which is lethal for adenylate-cyclase-positive host cells.