Sp1 binding is known to protect CpG islands from DNA methylation (19, 20), and the relatively weak binding of Sp1 to these P1 sites in Hodgkin’s lymphoma cells in which the promoter is suppressed led us to speculate that they could function as “road blocks” to prevent the methylation of P1 DNA in effector lymphocytes (12) [but see also Ref. This evidence concerns the gene SP1 and Hodgkins lymphoma.