VARIANTS OF THE HISTONE‐LIKE PROTEIN HGM IN THE TOXIC MARINE DINOFLAGELLATE GYMNODINIUM MIKIMOTOI (DINOPHYTA)

Wargo, M. J. 1 & Rizzo, P. J. 21 Department of Biology, HB 7560, Dartmouth College, Hanover, NH, 03755 USA; 2 Department of Biology, Texas A&M University, College Station, TX 77843 USA Gymnodinium mikimotoi, (formerly G. nagasakiense), is a unicellular toxin‐producing marine dinoflagellate, that lacks a cell wall. The absence of a cell wall, along with some other characteristics, makes G.mikimotoi an ideal dinoflagellate for nuclear studies. Consequently, we have developed a nuclear isolation procedure for this dinoflagellate, and identified a major histone‐like protein, HGm (Wargo & Rizzo, J. Phycol. 36, 584). Here, we present an electrophoretic analysis of HGm variants, including examination of these variants in response to certain environmental factors. The HGm protein group consists of four variants, termed HGm alpha 1, HGm alpha 2, HGm beta and HGm gamma. This determination was done using both one, and two‐dimensional gels. The two‐dimensional gel system utilized acetic acid/urea/Triton X‐100 (AUT)‐PAGE as the first dimension, and SDS‐PAGE as the second dimension. A comparison utilizing peptide mapping with V8 protease showed some similarity between the two alpha variants, and also between the HGm beta and HGm gamma, but not between the two different groups. These HGm variants also responded in a similar fashion to various environmental conditions tested, with the exception of nitrogen stress. Under conditions of very low nitrogen, HGm alpha 2 levels dropped lower than normal as compared to HGm alpha1 and HGm gamma, which merely matched the drop in total nuclear protein. Under these same conditions, HGm beta levels did not drop as drastically as the other HGm components or total nuclear protein. Thus the relative levels of these histone‐like protein variants do not appear to be influenced by the environmental conditions tested.