The complete nucleotide sequence of Spodoptera litura nucleopolyhedrovirus (SpltMNPV) Uba256 gene, encoding ubiquitin fused to GP37 protein of 256 amino acids was determined. The first 76 amino acids of the SpltMNPV ubiquitin showed 78-88, 77 and 81-84% amino acid sequence identity to baculovirus, Melanoplus sanguinipes entomopoxvirus and eukaryotes ubiquitins, respectively. The deduced amino acid sequence of SpltMNPV GP37 protein was similar to other baculovirus GP37 proteins and to entomopoxvirus fusolin proteins. The GP37 protein also showed a distant similarity to Pseudaletia separata entomopoxvirus enhancing factor, bacterial chitinase B and chitinbinding protein 1, but the significance of this is unclear. The mRNA start site of Uba256 fusion gene was mapped within a consensus baculovirus late promoter sequence (ATAAG), commonly found for baculovirus late genes. Uba256 transcripts were present from 48 h p.i. and remained detectable until 72 h p.i. Western blot analysis of SpltMNPV-infected Sl-zsu-1 cells revealed that the intact Uba256 was processed to free ubiquitin and GP37 protein. Whereas expression Uba256 gene in Escherichia coli did not result in processing of the fusion protein. Tunicamycin treatment of SpltMNPV-infected cells confirmed that SpltMNPV GP37 protein is N-glycosylated. These findings provide additional information on the evolution of ubi genes and insight into genomic variation in baculoviruses.