pBAC4x-1 is a baculovirus transfer plasmid designed for cloning and co-expression of up to four target genes or multiple copies of the same gene in insect cells. The plasmid contains two polh promoters and two p10 promoters, each of which is upstream of unique cloning sites for sequential insertion of target genes. The homologous promoters are in opposite orientations to minimize recombination. The plasmid is compatible with BacVector™-1000, -2000 or -3000 Triple Cut Virus DNA for low background transfection and efficient utilization of the promoters. The vector provides optional expression of a C-terminal His•Tag^® fusion sequence from the polh right-hand promoter by allowing read-through of inserts in the proper reading frame. Unique restriction sites are indicated on the circle map. The cloning/expression region of the coding strand transcribed from the clockwise promoters is shown below. The f1 origin is oriented so that infection with helper phage will produce virions containing single stranded DNA that corresponds to this strand. Single stranded sequencing of phage-derived DNA can be performed using the 1629DWN primer.