Unidirectional recruitment is essential for viral latency

Kaposi’s sarcoma associated herpesvirus (KSHV, HHV-8) is associated with several human malignancies. During latency the viral genomes reside in the nucleus of infected cells as large non-integrated plasmids, known as viral episomes. All KSHV infected cells express LANA, and LANA is essential for viral latency. LANA binding to the viral episomes is critical both for replication of the viral genomes during latency, and for tethering the viral episomes to the cell chromosomes during cell division. Directional recruitment of protein complexes are critical for proper function of many nuclear processes. To test for recruitment directionality between LANA and cellular proteins we directed LANA via catalytically inactive Cas9 (dCas9) to a repeat sequence to obtain easily detectable dots. Then, recruitment of nuclear proteins to these dots can be evaluated. We found that LANA recruited its known interactors ORC2 and SIN3A. Interestingly, LANA was unable to recruit MeCP2, but MeCP2 recruited LANA. Similarly, histone deacetylase 1 (HDAC1) that interact with the transcriptional-repression domain (TRD) of MeCP2, same as LANA, was unable to recruit MeCP2, but MeCP2 was able to recruit HDAC1. In contrast, HP1a that interacts with MeCP2 through a different domain, was able to recruit MeCP2. We propose that available interacting domains in DNA bound/dimerized form of MeCP2, forces this recruitment directionality. We found that cells derived from Rett syndrome and express a mutant MeCP2 (T158M), impaired in DNA binding, cannot support KSHV genome maintenance. Therefore, this unidirectional recruitment of LANA by MeCP2 identified MeCP2 as a critical factor for viral maintenance.