Herpes Simplex Virus Thymidine Kinase (HSV TK) PolyA Signal
Polyadenylation signal fragment from the 3' end of the herpes simplex virus type 1 (HSV-1) thymidine kinase (tk) gene. The 272 bp fragment carries two tandem AATAAA hexanucleotides and serves as a transcript 3'-end processing and polyadenylation signal in expression constructs.
Origin: Herpes Simplex Virus Type 1 (HSV-1) thymidine kinase gene
Characteristics
The stored 272 bp sequence contains two AATAAA copies, at positions 62-67 and 75-80, with 205 nt following the first copy. In HSV-1 tk deletion constructs transfected into Cos-1 monkey cells (S1 nuclease protection assay), efficient processing at the normal site persisted with 44-46 bp kept downstream of the first AATAAA. The region critical for processing lies 20-38 bp downstream of the first AATAAA and is G+T-rich.
Applications: Tested as the native 3'-end processing and polyadenylation signal of the HSV-1 tk gene in plasmids carrying an SV40 origin of replication, transfected into Cos-1 monkey cells and analysed by S1 nuclease protection. Its downstream sequence requirements were mapped by progressive deletion from the 3' end.
Limitations: Processing at the normal site falls when sequence downstream of the first AATAAA is cut to less than about 44-46 bp, and a cryptic polyadenylation site in pBR322 sequence is used instead. The cited papers give no efficiency comparison with bGH, SV40 or synthetic polyA signals, and no data outside Cos-1 cells.