The herpes simplex virus immediate early protein ICP27 encodes a potential metal binding domain and binds zinc in vitro.

The herpes simplex virus type 1 (HSV-1) immediate-early regulatory proteins ICP27 and ICP0 each encode putative zinc-finger metal-binding domains. We utilized the technique of metal chelate affinity chromatography to demonstrate that ICP27 and ICP0 were able to bind to zinc in vitro. This property was further exploited to purify ICP27 from extracts of HSV-1-infected cells. The purification procedure also revealed that ICP27 possessed single-stranded DNA-binding activity. Analysis of ICP27 truncated peptides produced by in vitro translation verified that the zinc-binding region of ICP27 resides in the carboxy terminal 105 amino acids spanning the putative metal binding motif. However, a specific configuration of cysteine and histidine residues in this region was not required for binding to occur as demonstrated by the ability of a frame-shift mutation to bind with an efficiency similar to wild type. The mutated peptide retained four histidine and cysteine residues but in a configuration different from the consensus proposed for zinc-finger motifs. Therefore, while the region spanning the metal binding domain of ICP27 is essential for both the activator and repressor functions, and ICP27 binds zinc in vitro, it is not clear whether zinc binding in vivo is necessary for function.