Transcription from all early adenovirus promoters is stimulated by a 289
amino acid phosphoprotein encoded in the pre-early transcription unit E1A. To determine if this
protein could act on a nonviral gene placed on the viral chromosome, adenovirus recombinants were constructed in which the rat
preproinsulin I gene, including its promoter region, was substituted in both orientations for E1A.
Preproinsulin mRNA synthesis from these recombinants was greatly stimulated after
infection of line 293 cells, which constitutively express E1A
protein, compared to HeLa cells, which do not. Expression of the
preproinsulin gene was also greatly stimulated when HeLa cells were coinfected with the recombinants and wild-type adenovirus or a mutant defective in a second E1A
protein, but much less so by
coinfection with a mutant defective in the 289
amino acid phosphoprotein. Much of the E1A-induced
preproinsulin mRNA had a 5' end at the same position as the
preproinsulin mRNA isolated from
insulinoma cells, but a considerable fraction had 5' ends mapping heterogeneously within several hundred
nucleotides of this site.
Preproinsulin mRNA was also detected in 293 cells but not HeLa or HEK cells after transfection of a plasmid containing the
preproinsulin gene with no adenovirus sequence. This indicates that there is no cis-acting adenovirus sequence required for E1A
protein stimulation of
preproinsulin transcription.
Infection of rat cells with adenovirus did not induce detectable
mRNA synthesis from the endogenous
preproinsulin I gene. These results demonstrate that the E1A
protein can induce expression of a nonviral gene when it is newly introduced into mammalian cells by
viral infection or transfection, but it does not induce the endogenous cellular gene.