Chapter I. Studies on Chromosomal RNA. Chapter II. Effect of Hydrocortisone on the Template Activity of Liver Chromatin

Citation

Dahmus, Michael Edward (1968) Chapter I. Studies on Chromosomal RNA. Chapter II. Effect of Hydrocortisone on the Template Activity of Liver Chromatin. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/APSP-5851. https://resolver.caltech.edu/CaltechETD:etd-10032002-102109

Abstract

Chapter I.

Chapter I of this thesis is concerned with the isolation and characterization of ascites chromosomal RNA. The isolation of rat ascites chromosomal RNA as well as some of its physical and chemical properties are described in Section 1. Chromosomal RNA is characterized by its small size, lack of amino acid acceptor activity, and, relative to transfer RNA, low content of methylated bases. It has a base composition similar to that of ascites ribosomal RNA and is not labeled when the cells are exposed to a short pulse of ³²P. An RNA (3S cytoplasmic RNA), with properties similar to those of chromosomal RNA but contained in the cytoplasm, has also been isolated.

Section 2 is concerned with the hybridization properties of ascites chromosomal RNA to denatured ascites nuclear DNA. Chromosomal RNA hybridizes to about 4% of ascites nuclear DNA and has no sites in common with ascites messenger RNA. 3S cytoplasmic RNA hybridizes to about 20 of ascites nuclear DNA and contains no sequences not also contained in chromosomal RNA. The 3S RNA contained in the nuclear sap is homologous to 3S cytoplasmic RNA. Therefore, it appears that a fraction of chromosomal RNA is confined to the chromatin while the remainder is homologous to an RNA contained in both the cytoplasm and nuclear sap.

Chapter II.

This chapter is concerned with the effect of hydrocortisone on the template activity of liver chromatin. Hydrocortisone administered to an adrenalectomized rat causes a two- to threefold increase in the rate of RNA synthesis in the liver. Chromatin isolated from the liver of hydrocortisone-treated rats possesses a 30 % greater template activity for DNA-dependent RNA synthesis than does chromatin isolated from control rats. The difference in template activity is abolished by removal of the proteins associated with the DNA. Hydrocortisone, administered to isolated purified chromatin, does not alter its template activity.

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