Parvovirus H-1 P38 promoter requires the trans-activation region (tar), an SP1 site, and a TATA box for full activity.

In the parvovirus H-1 P38 promoter, there are sequences identified as a TATA box, an SP1 site, and a trans-activation responsive element (tar). It was previously shown that the parvovirus H-1 nonstructural protein NS1 positively regulates the expression of the P38 promoter for the viral capsid protein gene via the tar. To characterize the tar element further, a series of single-point mutations of the tar was constructed and the mutants were compared to wild-type for the trans-activation of the P38 promoter using a cat reporter gene. Most of the tar mutations had a negative effect on the P38 promoter and some of them reduced activity as much as 70%. However, when several mutants with multiple-point mutations in the tar were tested, no significant additive effect was observed. We examined the function of the SP1 site in the trans-activation of the P38 promoter by replacing the wild-type SP1 sequence with synthetic DNA fragments, OSP1 or 2SP1, containing no SP1 or two SP1 sites respectively, in a P38 construct with a cat reporter gene. The results indicate that P38 expression varies in proportion to the number of SP1 sites, suggesting a role for the SP1 site during trans-activation by NS1. The role of the TATA box on the P38 promoter was also examined by mutagenizing TATA to CACG. The activity of this promoter was reduced to 43%. When a construct mutated at both the SP1 and TATA box sites was tested for its activity, about 22% of the wild-type activity remained, implying that this remaining activity was contributed largely by the tar element. A model is proposed for how the tar element activates the wild-type and SP1-TATA minus promoters in the presence of NS1.