trans-Activation of parvovirus P38 promoter by the 76K noncapsid protein.

The autonomously replicating parvoviruses contain a 5-kilobase linear single-stranded DNA genome that produces two noncapsid proteins, N1 and N2, and two overlapping capsid proteins, VP1 and VP2. To characterize the regulation of viral transcription, we began with a study of the promoter for the coat proteins (P38) at map unit 38. Various constructions containing the P38 promoter were fused to the bacterial gene for chloramphenicol acetyltransferase (cat), and the relative efficiency of expression was determined in the presence and absence of parvovirus gene products. Our results show that the P38 promoter is a weak promoter without a trans-activation mediated by the 76,000-molecular-weight (76K) N1 protein. The N1 protein, supplied either by superinfection with virus or cotransfection with the cloned N1 gene, increased greatly the expression of the P38 promoter. In addition, sequences 3' to the promoter, within the region + 127 to + 648 (assuming an mRNA start site at 2008), were required for optimal expression but not for trans-activation. These results suggest that the production of parvovirus capsid proteins is under the indirect control of the P4 promoter and one of its gene products.