The cell line KB18 constitutively expresses adenovirus type 2 (Ad2) early region 1B (E1B) genes in the absence of E1A expression and thus is useful for understanding the function and properties of E1B gene products. We report here that KB18 cells complement the cyt and deg phenotypes of Ad2 cytocidal (cyt) mutants and an Ad12 cyt mutant. Thus the E1B 19K polypeptide in KB18 is functional. Expression of E1B mRNA and synthesis of the 19K polypeptide were studied in wild-type Ad2- and Ad215-infected KB cells at 15 h post-infection, and in KB18 cells. Although E1B mRNA synthesized in KB18 cells at 5 to 7% of the level in Ad2-infected KB cells, the amount of E1B 19K polypeptide formed was similar. In contrast, the amount of 19K protein in Ad215-infected KB cells was about one-tenth of that in Ad2-infected cells, although expression of E1B mRNA was comparable to that during Ad2 infection. The half-lives of the 19K polypeptide in wild-type-infected KB cells, in Ad215-infected KB cells and in KB18 were approximately 90 min, 25 min and 22 h, respectively. The cyt phenotype was expressed at 30 to 35 h post-infection, thus showing that the instability of the 19K polypeptide in Ad215-infected cells is not due to alteration of cell morphology or cell destruction.


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