The H1
histones serve as general repressors of gene expression by inducing the formation of a compact
chromatin structure, whereas the high-mobility-group (HMG)
non-histone chromosomal proteins have roles in maintaining the structure and function of transcriptionally active
chromatin. The distribution of the H1
histone subtypes and
HMG proteins among various trout tissues (liver,
hepatocellular carcinoma, testis and erythrocyte) was determined.
Histone H1b was present in the
chromatin of liver, but not in the
chromatin of
hepatocellular carcinoma, testis or erythrocyte. Nuclease-resistant regions of liver
chromatin had elevated levels of
histone H1b.
Histone H1b was isolated, and the N-terminal amino acid sequence of
histone H1b was found to be highly similar to that of mammalian
histone H1(0) and duck H5.
HMG proteins T1, T2, T3, H6, C, D and F were associated with liver and
hepatocellular-carcinoma chromatin, with
hepatocellular carcinoma containing higher levels of HMG T1 and F. Testis and erythrocyte had HMG T2 and H6 as their predominant
HMG proteins. Most of the HMG H6 of
hepatocellular carcinoma, but not of liver, was located in a
chromatin fraction that was soluble at physiological ionic strength and enriched in transcriptionally active
DNA. These alterations in the
chromatin distribution and content of hepatocyte
HMG proteins and H1
histone subtypes may contribute to aberrant hepatocyte gene expression in the
hepatocellular carcinoma.