Overall strategy for preparation of cDNA libraries and routing of rearrayed clones to prepare drivers for subtracting new cDNA libraries. From small samples of tissue (i.e., <15 μg of total RNA as template), the resulting cDNA could neither be normalized nor subtracted. When at least 15 μg of starting total RNA was available, cDNA was subtracted with a driver derived from a minilibrary set and nonredundant rearrayed library. For larger tissues, cDNA was prepared from mRNA. In this case, cDNA was also normalized by using an aliquot of the starting mRNA together with the subtraction step. Any newly prepared libraries went through this routine, making libraries prepared at a later time more strongly subtracted than those prepared earlier.
