(A) Diagram of the hCG–PML-RARα transgene. Transcription begins at the arrow, the transcriptional start site of the hCG gene. The hCG sequences extend upstream approximately 2.4 kb from the start site. The solid black boxes represent the five exons of the hCG gene; the polyadenylation signal is provided by the hCG gene. Sizes of DNA fragments used in constructing the transgene are denoted below the diagram. (B) RT-PCR analysis of bone marrow RNA. The diagram illustrates the portion of the transgene-specific mRNA that is amplified. The sequences of the forward and reverse primers are also shown. PCR products that hybridize to an hCG exon 2-specific probe shown in the upper autoradiogram indicate the founder lines that express the transgene. In the lower autoradiogram, RNA quality is controlled using primers specific for endogenous mCG exon 4 and a probe specific for detecting these sequences. The RNA source and transgene status is indicated above each lane (founder line/transgene copy number: 67/5, 71/1, 72/15, 83/2, 126/1, 135/4, 137/1, 148/1).