Principle of the mRNA-tagging method. Step 1, FLAG-tagged poly(A)-binding protein (PABP) is expressed from a transgene using a cell-specific promoter. Step 2, PABP and poly(A)+ RNA are crosslinked in situ by formaldehyde. Step 3, poly(A)-RNA/FLAG-PABP complexes are purified by anti-FLAG affinity purification. Step 4, RNA-PABP crosslinks are reversed and RNA is isolated. Step 5, purified RNA is used for microarray analysis.