[Length of nucleosomal DNA repeat in whole cells, fixed by freezing in the presence of formaldehyde].

It is shown that whole cells can be effectively fixed in the presence of formaldehyde at -12 degrees C. This reaction is used for the study of the native structure of chromatin. In the nuclei isolated from fixed cells the chromatin has the nucleosomal structure. The size of nucleosomal DNA in these nuclei estimated by hydrolysis with staphylococcal nuclease does not differ significantly from repeat length in the nuclei fixed after isolation or in non-fixed nuclei. However it is shown that mono- and oligonucleosomes in the nuclei from fixed whole cells are significantly more stable to the exonucleolytic degradation than in either nuclei fixed after isolation or non-fixed nuclei. The results suggest that the nuclei isolation does not appreciably affect the chromatin structure. The fixation of whole cells by formaldehyde in frozen suspension can be used also to study the structure of other cellular components and macromolecular complexes directly in the whole cell.