A model for chromatin landscape in 5' regions of tissue specific and housekeeping genes. (A) depicts the repressive role of chromatin in maintaining tissue specific gene expression profiles in a chromosome. The chromatin organisation in the 5' regions of Tsg1 and Tsg2, two different tissue specific genes dispersed in the chromosome is shown. Nucleosome formation potentials and S/MARs – the boundary elements, are enriched in their upstream regions and might play a major role in facilitating tissue specific expression. This is likely to be a local effect since neighbouring genes might have a different expression pattern. (B) depicts the chromatin organisation in the 5' regions of Hkg1, Hkg2 and Hkg3, three housekeeping genes clustered in the chromosome. The presence of low nucleosome formation potential regions and enrichment of nucleosome destabilising elements ensure an open chromatin configuration in this domain. As Hkg generally cluster together, they are depleted in S/MARs relative to tissue specific genes as shown in the present analysis by the significant absence of predicted S/MARs in both 5' and 3' regions of housekeeping genes as compared to tissue specific genes.