Mapping of mouse transcription initiation sites by RLM-RACE. (A) Agarose gel electrophoresis of nested PCR reaction products from the RLM-RACE procedure using mouse NIH 3T3 RNA. Molecular size markers (base pairs) are indicated on the left. Arrows on the right mark the major PCR products. (B) Sequence of the mouse p27Kip1 gene upstream of the translation initiation codon. Vertical arrows above the sequence indicate transcription start sites identified by cloning and sequencing the RLM-RACE products shown in A. Horizontal arrows below the sequence indicate the gene specific primers used for the RLM-RACE procedure. The start codon is boxed. The sequence shown is derived from Genbank accession number U77915.