on sequences located in the upstream region (approximately -40 to -250) of these promoters. In addition, we showed that the major late and Ella late upstream promoter regions do not contain such Ela-responsive sequence elements. In contrast, after transfection of these chimeric promoter recombinants into 293 cells (which constitutively express the Eta proteins), we found that their relative levels of transcription are similar and markedly different from those observed when they are cotransfected into HeLa cells with Eta protein-producing recombinants. We conclude that the efficiency of transcription from a given promoter in 293 cells is not necessarily related to the presence of a specific Ela-responsive element.