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Mutations in neurofibromatosis type 1 target the gene coding for neurofibromin. While neurofibromin is able to accelerate the rate of GTP hydrolysis by cellular Ras proteins, its biological function is not well understood. To gain information regarding its function, the intracellular localization of neurofibromin was analyzed in cultured cell lines using polyclonal antisera raised against four neurofibromin-specific peptides, three from the carboxyl terminus and one from the amino terminus. In methanol-fixed cells distinct rod-like structures distributed throughout the cytoplasm were recognized by the antisera. Similar structures were seen with each antiserum, including affinity-purified antibodies, and in each of the cultured cell lines tested. Similar structures were seen in paraformaldehyde-fixed cells. Double staining experiments showed that these structures colocalize with mitochondria, but not with actin, beta-tubulin, or endoplasmic reticulum. When actin or tubulin structures within the cell were disrupted by separate antimitotic drugs, these stained structures retained their shape. Neurofibromin association with mitochondria was confirmed biochemically when highly purified mitochondrial fractions from bovine heart tissue were shown in Western analysis to contain neurofibromin. This association might be helpful in predicting identification of some of the cellular proteins with which neurofibromin interacts.

Fifty-five single-copy DNA probes were isolated from the library LL06NS01, which was constructed from a complete HindIII digest of a flow-sorted human chromosome 6. Because chromosomes from a human x Chinese hamster somatic cell hybrid were used as the starting material for the flow-sorting, the library could be expected to contain some contaminating Chinese hamster DNA as well as DNA from human chromosomes other than 6. Thirty-seven of the 55 probes, however, were shown to map to human chromosome 6 by Southern blot hybridization with DNA from a panel of somatic cell hybrids. Eleven of the probes were mapped further by in situ hybridization. Four probes were localized to the short arm of chromosome 6, six to the long arm, and one to the centromeric region.