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The structural gene for human acid β-glucosidase (GBA) has been regionally assigned to a narrow region on chromosome 1 using somatic cell hybridization, specific immunoprecipitation, and assay with the natural substrate. A human fibroblast line, 46, XX, del(1)(pter→q42:), was fused with mouse RAG fibroblasts and the heterokaryons were subcloned. All hybrid subclones containing a normal chromosome 1 were positive for GBA. In contrast, subclones with a single del(1) were negative for GBA by both immunoprecipitation and natural substrate assays. These results were consistent with the previous assignment of GBA to the region 1p11→qter and further localized the gene to the narrow region 1q42→qter.

Chromatin-DNA competition has been utilized to examine the general nature of chromosomal proteins interacting more strongly with BrdU substituted DNA. When chromatin is incubated with an excess of purified DNA, a portion of the chromosomal proteins will exchange to the purified DNA. These two complexes can then be separated on Metrizamide gradients due to their differing protein/DNA ratios. Using this technique we observe that most nonhistone chromosomal proteins will exchange to a competitor DNA, the extent of exchange being directly dependent upon the competitor DNA being present in excess. While essentially the same proteins will migrate to either unsubstituted or BrdU substituted DNA, the substituted DNA is found to be a quantitatively better competitor and its effectiveness as a competitor is directly related to the level of BrdU substitution. INTRODUCTIONThe observation that the thymidine analog, 5-bromodeoxyuridine (BrdU), will alter the expression of specific genetic loci in animal cells (1-4) is frequently considered to be related to the demonstration of Lin and Riggs that both structural and regulatory proteins will bind more tightly to substituted DNA. This phenomenon has been most extensively investigated by the filter

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