Screening expression yield of 24 well cultures by dot blot. Supernatants from 2 ml 24 well blocks transient transfections were analysed by Cy5 dot blot using denaturing conditions of 5 M urea. The top half of the blot represents supernatants from cells seeded at 5 × 105 cells/ml and the bottom half of the blot represents supernatants from cells seeded at 1 × 106 cells/ml. Dots showing secretion positive hits are indicated by a circle (14 positive hits and 9 failures). Those dots corresponding to successful purification hits from large scale transient transfections are shown by a square box around the vector number. The signal intensity of the dots is shown in table 2. The control protein C was rCD4 (domains 3 + 4)-His10 expressed from vector C, Figure 1.