Characterization of chromatin (nucleoid) from extreme halophilic archaeon Halobacterium salinarium H3 shows no nucleosomal organization

摘要

Halobacterium salinarium, a euryarchaeote, is a member of haloarchaea requiring at least 3.5 M NaCl for optimal growth. We intended to biochemically analyze the chromatin from this organism because of the reported nucleosomal structure of the chromatin. Chromatin (nucleoid) was isolated from H. salinarium H3. Nucleoid fractions isolated from the mid logarithmic and late logarithmic phase cells were separated into two peaks (peaks I and II) by sucrose density gradient centrifugation. Growth cycle dependent variation in the two chromatin Peaks was observed as reported earlier. DNA and protein compositions were determined for the isolated chromatin factions from both mid logarithmic and late logarithmic cells. Micrococcal nuclease digestion and agarose gel electrophoresis of the different chromatin factions showed absence of repeating units (nucleosome-like) of DNA protein complexes and DNA fragments did not resolve into DNA ladder pattern up on gel electrophoresis. Our results suggest that the chromatin of H. salinarium is more like bacterial and crenarchaeal chromatin and unlike that of other euryarchaeal chromatin from thermophilic methanogens which is organized like mini nucleosomes with the help of histone fold proteins (e.g. HMf).