Nucleotide sequence of a gene essential for viral DNA replication in the baculovirus Autographa californica nuclear polyhedrosis virus.

The nucleotide sequence of the 60.1- to 65.5-m.u. region of Autographa californica nuclear polyhedrosis virus (AcMNPV) was determined. Seven large open reading frames were identified. Two open reading frames potentially encoding gene products of 143 and 38 kDa were found in the counterclockwise direction upstream of the p6.9 gene. Four additional open reading frames were found in the opposite direction. Analysis of the predicted amino acid sequence of the 143-kDa gene revealed a potential leucine zipper motif, a putative nuclear localization signal, and seven amino acid motifs previously identified in a number of proteins involved in NTP binding and DNA/RNA unwinding. The mutation in a DNA replication defective temperature-sensitive mutant was fine mapped to the carboxy terminus of the ORF1(p143) gene. Sequence analysis of the mutation site identified a single base change of a guanine to an adenine, resulting in the substitution of a methionine for valine. This mutation resides seven amino acids downstream of the putative NTP-binding motif of the ORF1(p143) gene product and results in a DNA negative mutant. Together these data strongly suggest that the ORF1(p143) gene product is a baculovirus helicase.