Abstract

Micronuclei of Tetrahymena thermophila contain two electrophoretically distinct forms of histone H3. The slower migrating micronuclear species, H3S, is indistinguishable from macronuclear H3 by electrophoretic analyses in three gel systems and by partial proteolytic peptide mapping. The faster species, H3F, is unique to micronuclei. Pulse-chase experiments with radioactive amino acids show that H3S is a precursor to H3F. We present evidence that the in vivo processing of H3S into H3F requires cell growth and/or division and may occur regularly each generation at a specific point in the cell cycle. The processing event must occur after H3F is deposited on micronuclear chromatin, since both H3S and H3F can be isolated from sucrose gradient-purified mononucleosomes (Allis, Glover and Gorovsky, 1979). Partial proteolytic peptide mapping coupled with 3H-N-ethylmaleimide labeling suggest that the processing event involves a proteolytic cleavage from the amino terminal end of H3F. Automated sequence analyses of 14C-lysine-labeled macronuclear H3 together with either 3H-lysine-labeled H3S or H3F demonstrated that H3F is derived from H3S by a proteolytic cleavage which removes six residues from the amino terminus. These observations represent the first demonstration of a physiologically regulated proteolytic processing event in histone metabolism.

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.