The tegument protein UL94 of human cytomegalovirus as a binding partner for tegument protein pp28 identified by intracellular imaging

The tegument protein pp28 of human cytomegalovirus (HCMV) is essential for the assembly of infectious HCMV virions, but how it functions during the process of HCMV tegumentation and envelopment remains unclear. By using live cell fluorescence resonance energy transfer (FRET) microscopy and yeast two-hybrid assays, we found that another HCMV tegument protein, UL94, was a specific binding partner for pp28. The interaction between pp28 and UL94 was imaged in a punctuate, juxtanuclear compartment, previously designated as the virus assembly compartment (AC). Amino acids 22–43 of pp28 were identified as being responsible for its binding with UL94, while no linear binding site could be found within UL94. The interaction between pp28 and UL94 may serve as a link in the sequential processes of HCMV capsidation, tegumentation and envelopment. This study provides a foundation for further studies into how the HCMV tegument proteins act in the assembly of HCMV virions.