Analysis in Cos-1 cells of processing and polyadenylation signals by using derivatives of the herpes simplex virus type 1 thymidine kinase gene.

Bal31 nuclease was used to resect the herpes simplex virus type 1 thymidine kinase (tk) gene from its 3' end, and a plasmid, pTK206, was isolated that lacked the processing and polyadenylation signals normally found at the 3' end of the gene. The wild-type gene, pTK2, and pTK206 were each transferred to pSV010, a plasmid containing the simian virus 40 (SV40) origin of DNA replication, allowing replication and analysis of the patterns of transcription in Cos-1 cells. Fragments of DNA containing processing and polyadenylation signals from SV40 and polyoma virus were inserted into the 3' end of the resected tk gene, pTK206. We found that tk gene expression requires a processing and polyadenylation signal, that signals from SV40 and polyoma virus could substitute for the herpes simplex virus tk signal, and that considerable differences in the levels of tk mRNA were present in Cos-1 cells transfected by these gene constructs. In addition, tk gene expression was restored to a low level after the insertion of an 88-base-pair fragment from the middle of the SV40 early region. Processing and polyadenylation do not occur in the vicinity of this fragment in SV40, even though it contains the hexanucleotide 5'-AAUAAA-3'.