An Hz-1 insect virus (Hz-1V) late gene encoding, a predicted polypeptide of 51 kDa was isolated from a cDNA library and mapped to the HindIII-J region (40-44.6 map units) of the viral genome. The p51 gene was characterized by DNA sequence, Northern blot, and primer extension analyses. The 1,152 bp open reading frame (ORF) is transcribed as a 1.8 kb RNA between 8 and 18 h post-infection (hpi) with maximum expression at 12 hpi. Homology was not detected between the nucleotide sequence upstream of the p51 ORF and the baculovirus conserved late promoter element NTAAG. Primer extension analysis detected one major late transcription initiation site at -205 nucleotides relative to the start of the p51 ORF and seven minor late initiation sites at positions upstream of this primary site. Comparison of the upstream regulatory regions of the p51 gene and the Hz- 1V p34 late gene revealed a region of significant homology comprised of the 9 bp sequence TTATAGTAT. The primary p51 transcription initiation site and all p34 transcription initiation sites were mapped to different nucleotides within this nonanucleotide sequence. This 9 bp motif was not observed in the ORFs of these genes, and no significant homology was detected between this motif and the 5' regulatory regions of any other characterized genes. The results of our study suggest that this conserved sequence may serve an important role in the regulation of Hz-1V late genes.