Expression of unspliced NS1 mRNA, spliced NS2 mRNA, and a spliced chimera mRNA from cloned influenza virus NS DNA in an SV40 vector.

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.