DEVELOPMENT OF TRANSFORMING FUNCTION DURING TRANSDUCTION OF PROTO-RASINTO HARVEY SARCOMA-VIRUS

Oncogenic retroviruses are generated by transduction of the coding reg ion of a protooncogene and acquire genetic changes during subsequent r eplication. Critical genetic events which occurred during and after tr ansduction of rat proto-ras-1(Ha) into Harvey sarcoma virus were ident ified by evaluating the transforming activity of plausible synthetic p rogenitor proviruses encompassing the complete proto-ras genomic regio n with or without various 5' deletions. All progenitor proviruses indu ced phenotypic transformation of mouse NTH 3T3 cells, although with a 5- to 10-fold lower frequency than Harvey sarcoma provirus. Although n o tumor formation was observed in vivo after inoculation in the absenc e of helper murine retrovirus, both wild-type and progenitor viruses i noculated in the presence of helper virus induced tumors in newborn BA LB/c mice. No critical alterations of the p21(ras) coding region and n o deletion of 5' genomic elements were detected in a progenitor virus encompassing the complete proto-ras genomic region that had been isola ted from tumors. However, one progenitor virus that included all proto -ras exons induced tumors with a decreased latency. This virus contain ed a mutation in codon 12 (glycine to valine), which had apparently be en selected during tumorigenesis in vivo. During the genesis of Harvey sarcoma virus, critical steps conferring transforming function are th erefore transduction of coding proto-ras exons and enhancement of thei r transforming function by specific amino acid changes in p21(ras).