A soldered heat exchanger, in particular a condenser for motor vehicles which has at least one collector tube, and a flange which is secured to the collector tube and which is used to receive connection tubes. The gun body includes a gun body fluid passage in fluid communication with gun body inlets and the mixing manifold. The assembly unit comprises a device for determining activity of the seeds with an accuracy that allows distinguishing between different activities within tolerance ranges of specified nominal activities for the seeds. Also disclosed are methods of using the expression vector utilizing an internal polyadenylation signal, host cells transfected therewith, stable pools of cells transfected with an expression vector utilizing an internal polyadenylation signal, and clones of such transfected cells.