Influenza virus gene 8 codes for two nonstructural proteins (NS1 and NS2) which 
are translated, respectively, from a colinear and an interrupted mRNA. To 
investigate the mechanism of transcription processing by splicing, cloned 
full-length NS DNA was inserted into the late region of an SV40 vector. In this 
manner, transcription of NS RNA from the recombinant initiates and terminates 
using SV40 control sequences. RNA mapping and sequence analysis showed that the 
RNA transcripts are processed to produce both the spliced and unspliced NS mRNAs 
in approximately equal abundance. The junction sequence of the spliced mRNA is 
identical to that of NS2 mRNA found in influenza virus-infected cells. In 
addition, another mRNA species was found to contain a chimera splice between 
SV40 and NS sequences. Both NS1 and NS2 polypeptides are produced in the 
recombinant-infected cells as predicted from sequence analysis. These studies 
establish that during influenza virus infections processing of the NS1 mRNA 
transcript undergoes a mechanism of splicing similar to that occurring with 
DNA-directed RNA transcription.