Heterokaryons were made by fusion of alpha-L-iduronidase-deficient fibroblasts from patients with the Hurler, Scheie, or Hurler/Scheie compound syndrome. The fused cell populations remained alpha-L-iduronidase deficient and accumulated 35S-labeled glycosaminoglycans (35S-GAG) to the same extent as the parental cells strains. Also, when 35S-GAG accumulation was studied by autoradiography at the level of single bi- and multinuclear hybrid cells, no evidence was found for genetic complementation. The results support the hypothesis that the mutations in the Hurler and Scheie syndromes are allelic, and they are compatible with the view that patients with intermediate phenotypes represent genetic compounds.

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In this paper photoreactivation of UV damage in growing uvs ÷, uvsD53 and uvsE82 conidia of Aspergillus nidulans is examined. The results indicate that uvs + and uvsE82 conidia immediately start to lose photoreactivable lesions following incubation in the dark, but that uvsD53 conidia retain these lesions for at least several hours. The observations are interpreted as indicating that uvs + and uvsE82 conidia are excision-efficient but that uvsD53 is defective in excision repair.

A method is described for localizing acid mucopolysaccharides autoradiographically in cultured cells. Normal fibroblasts and fibroblasts, from patients suffering from Mucopolysaccharidosis II disease (MPS II), were cultured for six days in the presence of 35SO4 and one day in unlabelled medium. The cultured cells were transferred to plastic film dish and, after settling, they were rapidly quenched, freeze-dried, fixed in osmium tetroxide vapour and embedded in Epon. Grain counting after autoradiography in 2 mum sections revealed a significant difference (P greater than 0.001) in 35SO4 incorporation in the perinuclear cytoplasm of MPS II cells and control cells grown under the same conditions. Autoradiography was also performed after mixing MPS II cells and control fibroblasts in a ratio 1:1-8 prior to freezing and the same ratio was found between labelled and unlabelled fibroblasts. These results demonstrate the feasibility of the present autoradiographic technique for the detection of the acid mucopolysaccharide storage at the single cell level.