We have studied the nuclear distribution of the non-histone HMG-I protein by indirect immunofluorescence in several human and murine somatic cell lines and in growing mouse oocytes. We show that HMG-I, a high mobility-group protein which interacts in vitro with the minor groove of AT-rich B-DNA, is found exclusively in the nucleus and that this localization corresponds to a complex distribution. By comparing the HMG-I-dependent fluorescence signal with the chromatin density determined by Hoechst 33342 or propidium iodide staining, we present evidence for the existence of three HMG-I sub-populations whose contribution to the total fluorescence can be determined using a newly developed quantitative co-localization image analysis program: foci that correspond to regions of heterochromatin, intense dots located within decondensed chromatin, and a more diffuse component extending throughout the nucleoplasm. In addition, we show that these sub-populations differ in their sensitivity to nuclease digestion and in vivo displacement by the minor-groove binder Hoechst 33342. Finally, double immunolabeling of RNA polymerase II-dependent transcription and HMG-I shows that the intense dots are not correlated with sites of high transcriptional activity. We discuss the possibility that these three sub-populations reflect distinct and separable biological functions of the HMG-I protein.
Three distinct sub-nuclear populations of HMG-I protein of different properties revealed by co-localization image analysis
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C. Amirand, A. Viari, J.P. Ballini, H. Rezaei, N. Beaujean, D. Jullien, E. Kas, P. Debey; Three distinct sub-nuclear populations of HMG-I protein of different properties revealed by co-localization image analysis. J Cell Sci 1 December 1998; 111 (23): 3551–3561. doi: https://doi.org/10.1242/jcs.111.23.3551
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