POSITION EFFECT VARIEGATION MODEL OF CHRO MATIN COMPACTION

A position effect variegation (PEV) model of chromatin compaction is p roposed, based on the concept of a statistical distribution of compact ion protein (CP) molecules around compaction initiation centers (CICs) . The principles of the model are as follows: (1) CICs are present in both hetero- and euchromatin, and (2) different CP molecules interact not only with DNA but also with one another, forming a multimeric comp lex. When a certain level of DNA-protein binding is exceeded, heteroch romatic domains are formed. The model suggests that continuous and dis continuous chromatin compaction resulting from PEV is due to an irregu lar CIC distribution along the chromosome.