Sendai virus (family Paramyxoviridae) has a linear, single stranded, negative-sense, nonsegmented RNA genome.  The viral  RdRp consists of two virus-encoded subunits, a smaller one P and a larger one L.  When different inactive  RdRp mutants with defects throughout the length of the L subunit where tested in pairwise combinations, restoration of viral RNA synthesis was observed in some combinations. This positive L–L interaction is referred to as intragenic complementation and indicates that the L protein is an oligomer in the viral RNA polymerase complex.