Nucleotide sequence and transcriptional analysis of the polyhedrin gene of Spodoptera exigua nuclear polyhedrosis virus

Abstract

The nucleotide sequence of a 1.1 kbp fragment of the multiple nucleocapsid nuclear polyhedrosis virus (MNPV) of Spodoptera exigua (Se) containing the polyhedrin gene was determined. An open reading frame (ORF) of 738 nucleotides (nt) was detected. This ORF encoded a protein of 246 amino acids with a predicted M(r) of 29K. The nucleotide and amino acid sequences were compared with the sequences of eight other NPV polyhedrins. The SeMNPV polyhedrin protein was most closely related to S. frugiperda MNPV polyhedrin with differences in only five amino acids, and most distantly related to the Lymantria dispar MNPV polyhedrin. The size of the mRNA was approximately 1,000 nt, as determined by Northern blot analysis. Using primer extension assays and S1 nuclease mapping the transcriptional start and stop sites of the polyhedrin mRNA were located. The 5' regulatory sequence appeared to be 44 nt in length with the mRNA start site predominantly at the first A of the TAAG consensus start sequence. Two degenerate poly(A) signals were found immediately downstream of the translational stop signal. The transcriptional stop was located approximately 230 nt downstream from the translational stop signal, in an AT-rich sequence that appears to be common to all baculovirus polyhedrin genes. The SeMNPV polyhedrin mRNA does not appear to be polyadenylated.