H1 histone sub-type distribution and DNA topoisomerase activity in skeletal muscle of tumour-bearing rats

In an investigation of possible causes of the transcriptional defect which has been observed in muscles atrophying in response to tumour growth, the amounts of histone H1 subtypes and the activities of DNA topoisomerase I and II, factors which can affect the structural organisation of chromatin, were studied in nuclei of skeletal muscle of rats bearing a Walker 256 carcinoma. The H1 histones were separated by SDS/PAGE into three fractions, H1.1, H1.2 and H1o. The level of H1.2 but not that of H1.1 or H1o was increased in the tumour-bearing animal. Tumour growth did not affect the activity of either DNA topoisomerase I or II.