Molecular analysis of the trans-activating IE-2 gene of Orgyia pseudotsugata multicapsid nuclear polyhedrosis virus

A second immediate early (IE) regulatory gene of the baculovirus Orgyia pseudotsugata multicapsid nuclear polyhedrosis virus (OpMNPV) has been identified. The IE-2 gene which is homologous to the IE-N gene of Autographa californica MNPV was mapped to the HindIII A fragment of OpMNPV between 0.41 to 1.37 map units. The IE-2 gene codes for a predicted protein of 45,640 Da and analysis of the amino acid sequence shows that the protein has a highly basic amino terminal domain and a cysteine-rich domain that is similar to a zinc finger motif that is also found in the baculovirus proteins GC30 and PE-38. The IE-2 gene is expressed as a 1.3-kb transcript that was detectable by 0.5 hr postinfection (hr p.i.), reached maximum steady state levels by 6 hr p.i., and declined slightly by 48 hr p.i. Cis-acting 5' regulatory sequences were analyzed by deletion analysis of the IE-2 promoter linked to the reporter gene chloramphenicol acetyl transferase. Maximum expression was obtained when the IE-2 promoter contained sequence 275 bp upstream from the transcriptional start site. trans-Activation analysis revealed that IE-2 trans-activated the IE-1 promoter and in addition appeared to be autoregulatory.