We have continued our studies of chromatin structure in the neighborhood of expressed genes. The globin gene family in chicken erythroid cells serves as a model system in which it is possible to study the mechanisms associated with regulation of the individual members of the family during erythroid development. We have extended our studies of the properties of the general erythroid-specific factor GATA-1. We have shown that a small peptide containing one 'finger' region of GATA-1 is capable of binding tightly and specifically to its target DNA. Furthermore, this region can bind as either a zinc or iron complex, suggesting that in some organisms, members of this family might be iron proteins. We have extended our studies of stage-specific erythroid expression to the chicken embryonic globin gene. We find that there is a considerable decrease in the nuclear concentration of two trans-acting factors that we can show are critical to stage-specific expression of this gene, and that may account in large part for the difference in the behavior of the promoter in primitive and definitive lineage cells. We also have continued studies of the relationship between transcription and chromatin structure. We devised a method of determining the fate of nucleosome cores during transcription of nucleosome-covered DNA. We can show that the cores are displaced by the passage of SP6 RNA polymerase, but that they reform at sites elsewhere on the template. From the distribution of these sites, we eliminate several proposed models for propagation of transcription on chromatin templates, and propose our own. The results are consistent with a mechanism we had proposed earlier.
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