In a previous study, we have shown that a newly identified chromosomal protein, RMSA-1 (Regulator of Mitotic Spindle Assembly-1), identified and cloned using a human autoimmune, serum, is essential for mitotic spindle assembly; we proposed that RMSA-1 was a previously unknown physiological substrate for cdc 2 kinase. In the present study, we show that this protein is present in crane fly and is associated with the chromosomes of spermatocytes. A 31 kDa molecule in extracts from crane-fly nuclei, isolated from larvae, pupae and adults, reacts with affinity-purified anti-RMSA-1 autoantibody, shown by immunoblotting. The autoantibody reacts, as shown by immunofluorescence, with crane-fly spermatocyte chromosomes in prophase through anaphase of both meiosis-1 and meiosis-II but does not react with preprophase or telophase nuclei or with spermatid nuclei. In all meiotic stages, the crane-fly sex chromosomes stain more intensely than the autosomes. We conclude that, since RMSA-1 is present in insect and mammalian cells, it is conserved across a variety of animal species. Further, since RMSA-1 binds to chromosomes in meiotic cells, it also may be essential for assembly of the meiotic spindle.

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