Examples of expression of SLF (A) and c-kit (B) by RT-PCR in c-kit subsets of CD34⁺⁺⁺ cells in 1 representative of 4 experiments. RNA was extracted from cells and reverse transcription was performed. PCR for SLF was performed using a pair of primers as described in Materials and Methods, which generate 757-bp and 673-bp products, respectively, representing soluble and membrane-bound SLF (A). PCR analysis for c-kit was performed using a pair of primers as described in Materials and Methods, which generates a 360-bp product (B). β-Actin, used as internal control, was performed using a pair of primers as described in Materials and Methods, and generates an 838-bp product. RNA extracts from human stromal cells (NFF) were used as positive control (+), and PCR reaction reagents were used as negative control (−). Lanes 1 through 3 are samples from CD34⁺⁺⁺kit⁺⁺, kit⁺, and kit^Lo/−cells, respectively.