While infection of deep zone bovine articular chondrocytes with lentivirus encoding either Creb5(WT)-HA or a mutant form of Creb5 lacking the amino acids encoded by exon 9 (i.e., Creb5(Δ9)-HA) drove expression of nearly equal levels of HA-tagged protein (Supplementary Fig. 1e), Chromatin-Immunoprecipitation (ChIP)-PCR revealed that only Creb5(WT)-HA (and not Creb5(Δ9)-HA) was able to bind to the enhancers that drive Prg4 expression (Supplementary Fig. 1f). Here, PRG4 is linked to infection.