ABSTRACT
The availability of relatively efficient DNA sequencing techniques in the late 1970s and early 1980s and the development of infectious molecular clones provided the means to dissect the genetic basis of poliovirus attenuation. Meanwhile, it became obvious that the helper-dependent reverse genetics technology used for engineering orthomyxoviruses was limiting, and that a helper-independent methodology similar to that developed for the NNS group was required. The gene order controls their expression since transcription proceeds by initiation at a single transcriptional promoter, and genes proximal to this site are transcribed at higher levels than those distal from the promoter. Thus the most abundant protein in the infected cell is the viral nucleoprotein which is the first to be transcribed, and the least abundant is the polymerase protein, L, which comes last in the gene order. They tested their hypothesis using the rhabdovirus, VSV, and created a series of recombinant viruses in which gene orders were altered.
