The cryptomonad histone H4-encoding gene: structure and chromosomal localization.
Cryptomonads are unicellular flagellates whose plastids are surrounded by four membranes. A periplastidal compartment, containing eukaryote-type ribosomes, starch grains and a so-called nucleomorph, is located between the inner and outer membrane pairs. The nucleomorph has been shown to be the vestigial nucleus of a eukaryotic endosymbiont. In order to obtain more information about the chromatin structure of the nucleomorph and the host nuclear chromosomes, we studied the distribution of the histone, H4. H4 was not detectable in the nucleomorph by immunolocalization, thus supporting earlier findings by Gibbs [In: Wiesner et al. (Eds.), Experimental Phycology 1, 1990, pp. 145-157]. Likewise, no H4 DNA was demonstrable in the nucleomorph by Southern hybridization. Sequence analysis, and Southern and Northern blot data of a cryptomonad gene, H4, indicate an intermediate position for these genes between animals and plants.