Organization of multiple regulatory elements in the control region of the adenovirus type 2-specific VARNA1 gene: fine mapping with linker-scanning mutants.

The adenovirus type 2-specific virus-associated RNA 1 (VARNA1) gene is transcribed by eucaryotic RNA polymerase III. Previous studies using deletion mutants for transcription have shown that the VARNA1 gene has a large control region which is composed of several regulatory elements. Twenty-five exact linker-scanning mutations in the control region, from -33 to +77, of this gene were used for definition of the number and boundaries of these elements. The effects of these mutations on transcription and competition for transcription factors in human KB cell extracts revealed five positive regulatory elements. The essential element, which coincided with the B block, was absolutely required for both transcription and formation of stable complexes. A second element, which included the A block, was also required for both transcription and formation of stable complexes. Although this element is not as essential as the B-block element, together with the B-block element it may be necessary for formation of the most basal form of transcription machinery. Therefore, these two elements are the promoter elements in this gene. In addition, one possible element in the interblock region and two elements in the 5' flanking region were also required for efficient transcription, but they were moderately required for formation of stable complexes. Transcription of these mutants and the wild-type gene using an extract of 293 cells was stimulated at least threefold over that with the KB cell extract, as expected. Similar regulatory elements of this gene were revealed, however, when the 293 cell extract was used for transcription of these mutants, suggesting that the E1A-mediated specific transcription factors act on the transcription machinery in a sequence-nonspecific manner.