mRNA species and proteins of adenovirus type 12 transforming regions: identification of proteins translated from multiple coding stretches in 2.2 kb region 1B mRNA in vitro and in vivo.

Analysis of cytoplasmic RNA in Ad12-infected and -transformed cells showed that more than 20 mRNA species are transcribed from regions 1A and 1B. These mRNA species could be classified into four classes according to the extent to which they were expressed in infected and transformed cells under various conditions. The proteins synthesized from the major species of each of these mRNAs were identified by in vitro translation. In region 1A, the 40K (and 38K) proteins were synthesized from three mRNA species that differed from one another in their 5' ends, and in region 1B three proteins with molecular weights of 19,000 (19K), 50K, and 17K were synthesized from a single species of 2.2 kb mRNA. Only the 19K protein was immunoprecipitated by anti-T serum (G serum) from rats bearing GY1 cell tumors, [GY1 cells are rat cells transformed by the Ad12 HindIII-G fragment (0-6.8 map units).] The 19K protein was also detected by immunoprecipitation in extracts from both transformed and infected cells. The 17K protein was immunoprecipitated by anti-T serum (C serum) derived from rats bearing CY1 cell tumors, but was not by G serum. [CY1 cells are rat cells transformed by the Ad12 EcoRI-C fragment (0-16.5 map units).] The 17K protein was also translated in vitro from the 0.5 kb region 1B mRNA. These results suggest that the 19K and 17K proteins correspond to Ad12 T antigen f and polypeptide IX, respectively, and that these two proteins are translated in vivo from different coding regions in 2.2 kb mRNA in CY1 cells.