A 1.4 kb region downstream of the DNA polymerase gene of Autographa californica nuclear polyhedrosis virus was sequenced. Two open reading frames (ORFs) were identified of 927 and 474 bases in length. The 927 base ORF encodes a 34.8K protein as determined by in vitro translation of both hybrid-selected RNA and RNA synthesized in vitro from a 927 base ORF template. The predicted amino acid sequence of the 34.8K polypeptide (p34.8) reveals a hydrophobic N terminus, two potential N-glycosylation sites, and potential sites for phosphorylation by casein kinase I and protein kinase C. The p34.8 gene has a strong codon usage bias which is strikingly different from that of the polyhedrin gene. The two 5' ends of the 927 base ORF transcripts initiate from an ATAAG sequence and a GTAAG sequence 11 and 87 bases upstream of the ATG codon respectively. A short upstream reading frame is present in the leader sequence of the longer RNA. The transcripts have multiple 3' ends; the most proximal endpoint correlates with a polyadenylation signal overlapping the translational termination codon of the 927 base ORF. Transcripts of the latter were not observed early in the infection cycle but appeared 6 h after infection and were maximally expressed at 12 to 24 h post-infection. The late nature of these transcripts was confirmed by their sensitivity to aphidicolin and cycloheximide, inhibitors of DNA replication and protein synthesis respectively. Attempts to construct viral mutants carrying a deletion of the p34.8 gene and fusion with the beta-galactosidase gene suggest that the former gene is essential for viral replication.