Genes induced by IL-3 withdrawal. (a) Gene trap position in previously characterized genes. GTSTs were either obtained by 5'RACE or inverse genomic PCR. Exon/intron boundaries were either available from the databases or were determined by RT-PCR reactions using mRNA from FDCP1 cells and exon-specific primers. (b) Northern blot analysis of cellular genes induced by IL-3 withdrawal. Polyadenylated RNAs (5 μg per lane) extracted from FDCP1 cells at various intervals following IL-3 withdrawal were fractionated on formaldehyde-agarose gels, blotted onto nylon filters and hybridized to 32P -labeled gene- or exon (NET1)-specific probes. Blots were normalized with a 32P-labeled L32 probe. h, hours without IL-3.