Histone formation, gene expression, and zinc deficiency in Euglena gracilis

Histones, and other basic proteins, have been isolated from zinc-sufficient (+Zn) Euglena gracilis by standard chromatographic methods. These cells contain 2.46 micrograms of histones and 1.96 micrograms of DNA per 10(6) organisms. Each of the histones, H1, H3, H2A, H2B, and H4, is present in both log- and stationary-phase +Zn cells and has been characterized according to its electrophoretic mobility and molecular weight. H1 has been further identified on the basis of its amino acid composition and its cross-reactivity with calf thymus histone H1 antibodies. Similarly, H3 has been recognized as well by its specific reaction with an H3 antibody. In contrast, log-phase zinc-deficient (-Zn) cells contain H1 and H3 while H2A, H2B, and H4 are absent. All of the histones vanish in stationary-phase-Zn organisms. The DNA content increases as the -Zn cells progress from log to stationary phase, reaching a value of 4.40 micrograms/10(6) cells, double that of comparable stationary-phase +Zn organisms. A 2000-3000-dalton polypeptide whose electrophoretic behavior differs from that of the known histones constitutes over 90% of the total basic proteins of -Zn cells. On addition of zinc to stationary -Zn cells, cell division resumes, and all the histones and other basic proteins reappear. Together with previous results, the data demonstrate that zinc significantly affects the metabolism of all major chromatin components, i.e., the RNA polymerases, DNA, and histones of E. gracilis [Vallee, B.L., & Falchuk, K.H. (1981) Philos. Trans. R. Soc. London, Ser. B 294, 185-197]. The implications of these effects of zinc on chromatin structure and function are discussed.