Transcription start site mapping by RNase protection analysis of mouse p27Kip1 mRNA. (A) RNase protection of p27Kip1 mRNA derived from NIH 3T3 cells. The intact probe (lane 3) was 565 bases in length including mouse p27Kip1 sequences from 17 to 502 nucleotides upstream of the AUG and 79 nucleotides derived from vector sequences. Molecular size markers are shown in lane one and the size of each marker in nucleotides is indicated on the left. Lane 2 shows the protected fragments obtained using RNA from NIH 3T3 cells. The arrow at the right indicates the major protected fragment. The arrowhead and bracket indicate minor protected fragments. A control reaction using RNA derived from yeast is shown in lane 4. (B) RNase protection of p27Kip1 mRNA derived from mouse liver. Details are as described in A.