Two immunoglobulin kappa (Ig kappa) gene transcriptional control elements have been identified and characterized in considerable detail. One element, the Ig kappa promoter, is found upstream of all Ig kappa variable region genes. The other element, the kappa enhancer, lies in the intron that separates the joining from the constant region exons. The activity of the kappa enhancer controls kappa gene transcription at early stages of lymphoid development (i.e. the pre B cell stage). At this developmental stage the activity of the kappa enhancer is continually required for kappa gene transcription. At later stages of lymphoid development however, the properties of the kappa promoter and enhancer elements are insufficient to explain Ig kappa transcriptional control. At later stages of development Ig kappa transcription can continue in the absence of kappa enhancer activity. Therefore, there is a developmentally controlled transcriptional mechanism capable of maintaining kappa transcription in the absence of kappa enhancer activity. The mechanism of action and the DNA sequences responsible for this enhancer-independent transcription of Ig kappa genes are completely unknown. The long term goals of the research described in this proposal are to identify the DNA sequence requirements for enhancer-independent transcription and to understand the mechanism of action of this transcriptional control mechanism. Several parallel approaches to these problems will be utilized. One approach for identifying DNA sequences required for enhancer-independent transcription will take advantage of certain properties of somatic cell hybrids we have prepared. Other studies will focus on identifying specific chromatin differences between cell lines transcribing their kappa genes but differing in their ability to support enhancer-independent transcription. Mechanistically, the role of stably inherited chromatin alterations and the nuclear factors responsible for these alterations will be studied. Additionally, we will attempt to determine whether the mechanism of enhancer-independent transcription requires prior kappa enhancer activity, or whether it can activate transcription de novo. Finally, we will pursue studies relating to position- independent and copy number-dependent transcription of transfected Ig kappa genes.
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