Expression of the avian gag-myc oncogene in Saccharomyces cerevisiae.

The gag-myc oncogenic sequence of the avian retrovirus MC29 was first inserted in a multicopy expression vector allowing its expression in Saccharomyces cerevisiae. The oncogene transcripts were detected in yeast by Northern blot hybridization and gag-myc proteins were revealed by immunoprecipitation. On solid medium, the average size of gag-myc transformant colonies was smaller than control. In liquid cultures, the gag-myc strains had a doubling time of 4.7 h compared with 3.1 h in the controls. In one of the recipient strains, and after an initial transient period of 5 days, the gag-myc transformants became physiologically indistinguishable from control. In another recipient strain, the slow-growth phenotype is permanent. Plasmid instability is increased in gag-myc transformants. When a single copy of the gag-myc gene was inserted in a yeast chromosome, no phenotype was observed, showing that slow growth is the consequence of plasmid loss.