Direct sequencing of baculovirus genomic DNA: sequence determination of the engineered respiratory syncytial virus chimeric FG gene.

Primer-directed enzymatic sequencing has proven to be an efficient and effective method for sequencing various size double-stranded DNA templates. We previously developed a primer-directed sequencing procedure for using double-stranded cosmid (50 kb) DNAs as template. We are interested in using this method to directly sequence larger DNA templates. Towards this goal we applied this method to directly sequence an engineered gene that had been transferred and integrated into the 130-kb baculovirus genome. Both crudely prepared and CsCl gradient-banded baculovirus DNAs were tested and reasonable sequencing ladders were obtained for both types of DNA templates. As little as 3 micrograms of gradient-banded baculovirus DNA were found to be sufficient to obtain film exposure times similar to those observed for cosmid size templates, 24 to 48 h. Effectiveness of the described method was demonstrated by obtaining the complete sequence of the engineered respiratory syncytial virus chimeric FG gene (2.5 kb in length) directly from the recombinant baculovirus "Baculo-FG" genome. Thus, our results demonstrate first, that double-stranded DNA templates as large as 130 kb can be sequenced directly and second, that the nucleotide sequence of engineered genes integrated within the baculovirus genome can be determined without the use of any intermediate steps of procedures.