Transcriptional analysis of a major capsid protein gene from Spodoptera exigua ascovirus 5a

The major capsid protein (mcp) gene of Spodoptera exigua ascovirus 5a (SeAV-5a) was confirmed by aphidicolin viral DNA replication inhibition analysis to be a late gene. The 5' and 3' ends of mcp gene transcripts have been mapped. Primer extension analyses indicated that transcription of the mcp gene initiates from a cytosine 25 nucleotides (nt) upstream of the translation start codon. Two independent approaches by 3' rapid amplification of cDNA ends (3' RACE) and oligo (dT) cellulose binding assay suggested that SeAV-5a mcp mRNA is polyadenylated. Analyses by 3' RACE also revealed that mcp transcripts terminate at a U, either at 26 or 38 nt downstream of the translation stop codon. The putative 5' transcription control region of the SeAV-5a mcp gene shares similarities with other ascoviruses and Chilo iridescent virus (CIV), containing a conserved TATA-box-like motif (TAATTAAA) and an ATTTGATCTT motif upstream of it. The 3' downstream regions of the mcp gene of all the ascoviruses examined and CIV can form a stem-loop structure, and the ends of the mcp gene transcripts of SeAV-5a are within the predicted stem-loop region. This suggests that the stem-loop structure of the mcp gene might be involved in transcription termination.