Before revision: Proposed by R. J. Britten and E. H. Davidson in 1969, the model postulates four classes of protein sequences : an integrator gene, a producer gene, a receptor site, and a sensor site.
After revision: Proposed by R. J. Britten and E. H. Davidson in 1969, the model postulates four classes of genomic DNA region : an integrator gene, a producer gene, a receptor site, and a sensor site.