Isolation and partial sequence of the cyanogen bromide peptides from calf thymus non-histone chromosomal protein HMG 1

The amino acid sequence of a small DNA binding protein from the archaebacterium Sulfolobus solfataricus

The thermoacidophilic archaebacterium Sulfolobus solfataricus possesses several DNA binding proteins which may have a histone-like function. Two particularly dominant species have molecular masses of 7 and 10 kDa, respectively. We have purified one of the small proteins which occurs in relatively large amount and have determined its amino acid sequence. The protein is characterized by a high lysine content; in the N-terminal region the lysine residues occur in an alternating order: X-K-X-K-X-K-X-K. The amino acid sequence does not indicate any obvious homology to those DNA binding proteins whose sequences have been determined.

Uncoordinate synthesis of histone H1 in cells arrested in the G1 phase

It has been known for several years that DNA replication and histone synthesis occur concomitantly in cultured mammalian cells. Normally all five classes of histones are synthesized coordinately. However, mouse myeloma cells, synchronized by starvation for isoleucine, synthesize increased amounts of histone H1 relative to the four nucleosomal core histones. This unscheduled synthesis of histone H1 is reduced within 1 h after refeeding isoleucine, and is not a normal component of G1. The synthesis of H1 increases coordinately again with other histones during the S phase. The DNA synthesis inhibitors, cytosine arabinoside and hydroxyurea, block all histone synthesis in S-phase cells. The levels of histone H1 mRNA, relative to the other histone mRNAs, is increased in isoleucine-starved cells and decreases rapidly after refeeding isoleucine. The increased incorporation of histone H1 is at least partially due to the low isoleucine content of histone H1. Starvation of cells for lysine resulted in a decrease in H1 synthesis relative to core histones. Again the ratio was altered on refeeding the amino acid. 3T3 cells starved for serum also incorporated only H1 histones into chromatin. The ratio of different H1 proteins also changed. The synthesis of the H1(0) protein was predominant in G0 cells, and reduced in S-phase cells. These data indicate the metabolism of H1 is independent of the other histones when cell growth is arrested.

Loss of chromosomal high mobility group proteins HMG1 and HMG2 when mouse neuroblastoma and Friend erythroleukemia cells become committed to differentiation

Chromosomal high mobility group (HMG) proteins HMG1 and HMG2 from mouse neuroblastoma cells and Friend erythroleukemic cells were analyzed by acetic acid/urea/polyacrylamide gel electrophoresis. Compared to rapidly growing cells, levels of HMG1 and HMG2 were decreased in mouse neuroblastoma cells that had been induced to differentiate by serum deprivation. This comparison revealed a reciprocal relationship between these HMG proteins and H10, a histone known to be in higher concentrations in nondividing cells. When cell growth was inhibited by means of density inhibition, however, HMG1 and -2 levels were not affected in either HeLa or mouse neuroblastoma cells, even though H10 did not accumulate. This observation establishes that HMG1 and -2 contents are not correlated with mitotic rate per se. Treatment of mouse neuroblastoma by sodium butyrate, which stops cell division without commitment to differentiation, had no effect on the level of HMG1 and -2. However, the level was decreased by dibutyryl cyclic AMP and dimethyl sulfoxide treatments, which, like serum deprivation, induced irreversible morphological differentiation in the neuroblastoma cells. Moreover, induction of differentiation (hemoglobin synthesis) in Friend erythroleukemic cells by dimethyl sulfoxide showed a decrease in the contents of HMG1 and -2. These observations suggest that preferential loss of HMG1 and -2 in mouse neuroblastoma and Friend erythroleukemia cells may be related to commitment of these cells to differentiation.

Localization of chromosomal protein HMG-1 in polytene chromosomes of Chironomus thummi

The distribution of accessible antigenic sites in the chromosomal protein high mobility group one (HMG-1) in Chironomus thummi polytene chromosomes is visualized by immunofluorescence. The results indicate that (a) HMG-1 is distributed in a distinct banding pattern along the entire length of the chromosomes; (b) the banding pattern obtained with fluorescent antibody does not strictly correspond to that observed by phase-contrast microscopy; and (c) the amount of HMG-1 increases, and the fluorescent banding pattern changes, during the development of the organism. Our findings suggest that the protein may be involved in the modulation of the structure of selected loci in the chromosome.

Repeating oligonucleosomal units. A new element of chromatin structure

Supranucleosomal chromatin structure has been analysed by the use of histone H1 polymers crosslinked in nuclei and extended chromatin with bifunctional reagents methyl-4-mercaptobutyrimidate (MMB) and dimethyl suberimidate dihydrochloride. Almost pure H1 homopolymers were obtained in milligram amounts and examined for the distribution in molecular weights. The H1 homopolymer molecules both from nuclei and chromatin have been found to be integer multiples of an elementary structure (called "clisone") consisting of 12 histone H1 molecules. This finding strongly suggests that nucleosomal chains of chromatin are not uniform but rather organized as repeating oligonucleosomal units each consisting of 12 nucleosomes. Correlation between oligonucleosomal structures in nuclei and chromatin implies that a linearized nucleosomal chain retains the information on chromatin superstructure. The relation of the disclosed 12-nucleosome units to superbeads (nucleomeres) and other structures is discussed.

The isolation, characterization and partial sequence of a peptide rich in glutamic acid and aspartic acid (HGA-2 peptide) from calf thymus non-histone chromosomal protein HMG 2. Comparison with a similar peptide (HGA-1 peptide) from calf thymus non-histone chromosomal protein HMG 1

A 41-residue peptide (HGA-2) containing a continuous sequence of 35 glutamic and aspartic residues was isolated from non-histone chromosomal protein HMG 2. This highly acidic peptide is compared with a similar peptide (HGA-1) isolated from non-histone chromosomal protein HMG 1.