Proteolytic processing of h1-like histones in chromatin: a physiologically and developmentally regulated event in Tetrahymena micronuclei.

Abstract

Micronuclei isolated from growing cells of Tetrahymena thermophila contain threeHl-like polypeptides ¢~,/~, and % Micronuclei isolated from young conjugating cells (3-7 h) also contain a larger molecular weight polypeptide, X, which is being actively synthesized and deposited into these nuclei (Allis, C. D., and J. C. Wiggins, 1984, Dev. Biol., 101:282-294). Pulse-chase experiments (with growing and conjugating cells) suggested that X is a precursor to a and that a is further processed to ~, and a previously undescribed and relatively minor species, 6. These precursor-product relationships were supported by cross-reactivity with polyclonal antibodies raised against a and peptide mapping. While ~ consistently became labeled under chase conditions (both in growing and mating cells), it was not clear whether it is part of the in vivo processing event(s) which interrelates X, a, % and 6./~ was not recognized by ~ antibodies. Despite this uncertainty, these results suggest that proteolytic processing serves to generate significant changes in the complement of Hl-like histones present in this nucleus.

Epigenetics of Ciliates

“…Consistent with the fact that the macronucleus divides by amitosis, the macronucleus is devoid of Cnp1p (Cervantes et al 2006;. In addition to the different complement of core histone variants, the macro-and micronucleus contain different linker histones, the macronuclear linker histone H1 (Hho1p) and the micronuclear linker histone (micLH; Allis et al 1984;Wu et al 1986;Hayashi et al 1987). Neither linker histone gene is essential for cell viability, but individual gene knockouts result in an increase in volume of the nucleus in which each acts.…”

Effect of heat shock on ribosome structure: appearance of a new ribosome-associated protein.

“…The transfer solution used contained 12.5 mM Tris, 96 mM glycine, 0.05% SDS, and 10% methanol. Transfers were typically carried out at 0.6 A for 2 h. Antigen-antibody reactions and the visualization of those complexes with peroxidase-coupled goat anti-rabbit serum were carried out exactly as described by Allis et al (1).…”

Formaldehyde cross-linking and immunoprecipitation demonstrate developmental changes in H1 association with transcriptionally active genes.

“…Macronuclei contain a very lysine rich protein with solubility properties, secondary modification, and amino acid composition of Hi but which lacks features of the central globular domain typical of metazoan Hls (38). Micronuclei contain four incompletely characterized linker-associated peptides that are distinct from Hi (1,2). Thus, in T. thermophila as in other organisms, there is evidence suggesting that differences in linker histones are associated with marked differences in transcriptional competence.…”