Fine mapping of the p90 binding site. A Restriction map of the Hin dIII – Ava I region of c-mos 3'UTR cDNA. The position of the Xho I site introduced by mutagenesis is also indicated. Numbering is from the translation stop codon in the complete mRNA. B UV crosslink analysis of 32P-GTP-labeled transcripts that contain sequence information from different portions of the Hin dIII-Ava I regions of the c-mos 3'UTR cDNA, as indicated above the lanes. The position of the p90 protein is indicated on the right and the sizes of the molecular weight markers (lane 1) are indicated on the left. C The sequence of c-mos 3'UTR contained between the Hin dIII – Ava I restriction sites in the cDNA. The introduced Xho I site is underlined. The portion required for p90 binding is indicated in bold type.