The MPSS technique occurs in two major steps. In the first step, in vitro cloning of cDNA fragments on microbeads occurs. cDNA fragments are cloned onto microbeads using the Lynx Megaclone technology. Starting with one million mRNA molecules from a particular cell or tissue sample, Megaclone will produce one million beads, each containing 100,000 cloned copies of cDNA from each mRNA molecule. All molecules are covalently attached to the microbeads at their poly(A) ends, so the DpnII end is available for the sequencing reactions.
The image on the right illustrates the in vitro cloning of cDNA fragments on microbeads. The procedure involves both microbead tagged vector library preparation and sample preparation.