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Enhancement of RNA Synthesis in Chick Liver by Food Intake: Possible Role of High Mobility Group Nonhistone Proteins

Tatsuzo Oka, Joon Pyo Han, Yasuo Natori¹, Norihiko Hasegawa^*, Miharu Kanai and Nakazo Watari

Department of Nutritional Chemistry, School of Medicine, The University of Tokushima, Tokushima 770 ^* Department of Research, Chubu Rosai Hospital, Minato-ku, Nagoya 455 First Department of Anatomy, School of Medicine, Nagoya City University, Mizuho-Ku, Nagoya 467, Japan

RNA synthesis in the nuclei of liver from newly hatched (4-d-old) chicks is enhanced by intake of food. The enhanced synthesis was ascribed not to an increase in the activity of solubilized DNA-dependent RNA polymerase but to an increase in the initiation of RNA synthesis. Enhanced RNA synthesis in fed chicks was accompanied by greater susceptibility of nuclei to digestion by micrococcal nuclease. Salt extraction abolished the difference in nuclease sensitivity between the fed and fasted groups. Reconstitution with either 0.35 M NaCl extracts or high mobility group (HMG) nonhistone proteins restored digestion susceptibility, but changing the source of extracted proteins did not equalized the extent of digestion in nuclei from livers of fed and fasted chicks. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of HMG proteins revealed the presence of HMGs 1 and 2 as well as a 38,000-dalton protein. The nuclear HMG protein content in fed chicks was greater than that of fasted chicks (121 ± 17 µg/mg DNA vs. 31 ± 12 µg/mg DNA). The electron microscopic examination of hepatocyte nuclei revealed the enlargment of nucleoli and scarcity of aggregated heterochromatin structures in the fed chicks as compared with the fasted chicks. These morphological features are compatible with the high transcriptional activity in liver of fed chicks.

KEY WORDS: • RNA synthesis • chick liver • high mobility group (HMG) protein • chromatin structure

¹ To whom correspondence should be addressed.

Manuscript received 20 November 1984. Revision accepted 5 August 1985.