We have investigated binding of the lectins wheat germ agglutin (WGA) and concanavalin A (Con-A) to mitotic chromosomes and interphase nuclear substructures using fluorescein and rhodamineconjugated lectins. Standard cytogenetic preparations of human lymphocyte chromosomes were incubated with WGA. Mitotic chromosomes and interphase nuclei are brightly fluorescent. Con-A did not detectably bind chromosomes prepared in this way. Mitotic chromosomes display a distinctive banding pattern with WGA similar to quinacrine banding. We also studied binding to interphase "nuclear scaffolds", which are prepared by treating isolated Hela cell nuclei with DNAse l and high salt. WGA binds nuclear scaffolds internally while Con-A binds to the periphery. The specific binding of lectins to chromosomal structures derived from these two different methods indicates that glycosides are true chromosomal components and that glycoproteins may have a role in chromosome organization.
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The possibility remains that the component binding WGA is nonspecifically absorbed to the chromosomes during preparation. This seems unlikely due to the specific banding pattern seen in early stages of condensation. In addition, we have observed lectin binding to nuclear scaffolds, which are isolated in an entirely different way. We call the residual nuclear structure "nuclear scaffolds" because of their appearance, their lack of chromosome fibers (histones and DNA) and because they are composed of a set of about six major protein components similar to those in the "mitotic chromosome scaffold" previously described (Adolph et al., 1977). We have treated these structures with Con-A and WGA identically as cytogenetic preparations of chromosomes and have found that WGA binds primarily internal nuclear components, while Con-A binds the periphery. Thus lectin binding components are present in chromosomal structures prepared in different ways. The significance of the presence of Con-A binding sites at the periphery of nuclear scaffolds and their absence in cytogenetic preparations of mitotic chromosomes is not clear. However, the presence of WGA binding sites in both structures and their distribution in a banding pattern at mitosis suggest a role in the structural organization of chromosomes, Acknowledgements This work was supported by grants from the Graduate School of the University of Minnesota and the Leukemia Task Force, by grant no. CA 21463 from the N.I.H., and by grant no. PCM-7906505 from the NSF.