Effect of salt-treatment on manually isolated polytene chromosomes from Chironomus tentans

A method for the rapid manual isolation of polytene chromosomes and nuclear membranes from salivary glands of Chironomus tentans is presented and the analysis of some of their RNA and protein components before and after treatment with 2 M salt solutions is summarized.--After salt-incubation the chromosomes still display a considerable number of bands which stain with ethidium bromide and which are sensitive to treatment with DNase, RNase, trypsin, and proteinase K, to a lesser extent with pronase and papain. Analysis of the iodinated residual proteins on SDS gels yield three major and two minor bands (MW between 50,000 and 70,000 dalton) which were also shown to be present in interphase chromosomes of Ehrlich ascites cells which had been treated similarly and are also tightly bound constituents of DNA prepared according to Gross-Bellard et al. (1973). This result indicates the existence of a general class of non-histone proteins involved in keeping the DNA in a supercoiled state. Furthermore their presence in salt-treated nuclear membranes of Chironomus salivary gland cells (and Xenopus oocytes, unpubl.) will be of interest with respect to functional aspects of the nuclear matrix.