Removal of a 67-base-pair sequence in the noncoding region of protooncogene fos converts it to a transforming gene.

Abstract
Transformation of fibroblasts by protooncogene fos (c-fos) requires the linkage of viral long terminal repeat (LTR) sequences and interruption of 3''-noncoding sequences. An A+T-rich stretch of 67 nucleotides was identified, located 627-693 base pairs downstream from the coding domain and 123-189 base pairs upstream from the putative poly(A) addition site, removal of which confers transforming activity to the c-fos gene. A novel regulation of the expression of the c-fos gene is proposed, which may be functional in vivo to prevent the gene from becoming an oncogene.