Deletion mapping of tumor promotion-susceptibility gene pro1 implicates an RNA polymerase III transcription unit

The murine gene pro1 has been cloned from JB6 epidermal cell lines that are sensitive to neoplastic transformation by tumor promoters. Insensitive JB6 variants acquire susceptibility to neoplastic transformation by tumor promoters when transfected with pro1. The repetitive nature of pro1 was indicated by sequence and Southern analysis. In contrast, northern analysis of RNA from promotion-sensitive cells revealed the presence of a small pro1-hybridizing transcript. Strand-specific RNA probes implicated an RNA polymerase III (RNAPIII) coding domain in pro1 as the source of this hybridization signal. Ribonuclease protection of gel-purified pro1 RNA from JB6 variant cell lines identified a 130-nucleotide transcript. The size of this transcript is compatible with in vitro RNAPIII transcription of pro1. Deletion mapping of pro1 by exonuclease III demonstrated that the biologically active domain included the RNAPIII transcription unit. RNA probes map pro1 RNA within the activity domain. These results delineate an activity domain of 597 nucleotides and suggest that a small RNA is the product of promotion-sensitivity gene pro1.