CHROMATIN STRUCTURE AND TRANS-ACTIVATION OF HUMAN GLOBIN GENES

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Chromatin structure and trans-activation are two important aspects of gene regulation. Chromatin from actively transcribed genes exhibits a structure different from that of non-transcribed genes. It has been shown that trans-acting proteins can bind to DNA and confer a unique chromatin structure, and such a protein DNA interaction has been suggested to play an important role in gene regulation. In an attempt to investigate the mechanisms of regulation of human globin gene expression two approaches have been used: 1) We have studied the chromatin structure around the human beta-globin gene in K562 cells by using DNase I and S1 nuclease. Despite the beta-globin gene not being expressed, we found nuclease hypersensitive sites in both its 5' and 3' flanking regions. While the 3' hypersensitive sites are identical to that of active beta globin genes, the 5' hypersensitive sites shift further upstream. This suggests that the lack of beta-globin expression in K562 cells may be related to unique aspect(s) of the chromatin structure in the immediate 5' flanking region of the beta-globin gene. 2) To investigate the mechanism of trans-activation, globin promoters were tested in a transient expression system. We found that the globin promoter can be activated by SV40 T antigen in monkey kidney CV-1 cells. This trans-activation can be further stimulated by including a SV40 enhancer in the globin plasmid. The mechanism of the trans-activation is currently under study.