A time-course study of MuLV env gene expression in the AKR thymus: qualitative and quantitative analysis of ecotropic and recombinant virus gene products.

Low levels of synthesis of two species of MuLV env gene polyprotein (PrENV protein) in thymocytes of 3-month-old AKR mice were identified. Synthesis of PrENV proteins which comigrate with those of ecotropic and recombinant, dualtropic MuLV represented, respectively, 0.03-0.05 and 0.01-0.03% of total cell protein synthesis in these animals. An increase in the rate of synthesis of both PrENV species was observed in animals at 5-6 months of age; ecotropic virus PrENV represented 0.2-0.6% of total protein synthesis and recombinant virus PrENV, 1-2.5% of total protein synthesis in thymocytes of mice of this age. This same increase in env gene expression of both the ecotropic and recombinant virus was induced in 3-month-old animals by intrathymic injection of recombinant MuLV at 4-6 weeks of age. The level of recombinant virus env gene synthesis in thymomas was similar to that observed in thymocytes of 5- to 6-month-old animals and in experimentally injected animals; elevated synthesis of ecotropic virus PrENV protein was detected in 85% of these leukemias. Partial protease digest mapping of the recombinant virus PrENV protein isolated from 23 primary thymomas revealed that the predominant type of recombinant (18/23) expressed in these cells was that of the MCF 69L1/247 type. A notable finding was the identification of expression of variant ecotropic MuLV in these thymomas. Of ten leukemias studied, eight expressed ecotropic virus PrENV proteins which were distinguishable from that of Akv virus. Four unique ecotropic virus PrENV proteins were observed.