Contrary to the predictions from the current models of Rap1, we found no influence of the Rap1 binding site version on the kinetics of establishing silencing, nor on the maintenance of silencing, nor the extent of silencing.
The silencing of USP19 was also growth-inhibitory in 22RV1 cells (Fig. S1A), but not in LNCaP cells despite a similar extent of silencing of USP19 (Fig. S1B).
The extent of silencing appeared determined by sex chromosome complement independent of gonadal sex [ 60].
The extent of silencing varied in the different transformants between high and moderate levels.
Previous studies have mostly analysed PRDM5 transcript expression as a measure of the extent of silencing [ 2, 4, 8, 35].
The heterogeneity and reduced extent of silencing on autosomes are evidence for the importance of DNA elements underlying the spread of silencing.
Generally, the extent of silencing was greatest close to the translocation breakpoint; however, silencing was detected well over 100 kb into the autosomal DNA.
> -wrap-foot> Thus, we observed both DNA sequence and epigenomic differences correlated with the extent of silencing on the autosomal portion of t(X A)s.
To determine the requirements for efficient silencing we have analysed the relationship of chromosome features, including L1 repeats, and the extent of silencing in cell lines carrying inducible Xist transgenes located on one of three different autosomes.
This screen uses a GFP transgene that is particularly sensitive to epigenetic silencing, to identify genes elsewhere in the genome that when mutated alter the extent of silencing at the transgene locus (Blewitt et al. 2005).
Furthermore, direct interaction of HP1 and KAP-1, as well as binding of HP1 to H3K9me3, is necessary for the full extent of silencing mediated by these factors [ 57- 61].
