We introduce a novel model of nonsegmented negative-strand RNA virus (NNSV) transcription. Previous models have relied on polymerase behavioral differences in the highly conserved intergenic sequences. Our model hypothesizes the transcriptional gradient in NNSVs is explained through a simple model with two parameters associated with the viral polymerase. Most differences in expression can be attributed to the processivity of the polymerase while additional attenuation occurs in the presence of overlapping genes. This model reveals a correlation between polymerase processivity and genome length, which is consistent with the universal entry of polymerases through the 3' end of the genome. Using this model, it is now possible to predict the transcriptional behavior of NNSVs from genotype alone, revolutionizing the design of novel NNSV variants for biomedical applications.