Strong nucleosomes reside in meiotic centromeres of C. elegans

Abstract

Recently discovered strong nucleosomes (SNs) are characterized by strongly periodical DNA sequence, with visible rather than hidden sequence periodicity. In a quest for possible functions of the SNs, it has been found that the SNs concentrate within centromere regions of A. thaliana chromosomes . They, however, have been detected in Caenorhabditis elegans as well, although the holocentric chromosomes of this species do not have centromeres. Scrutinizing the SNs of C. elegans and their distributions along the DNA sequences of the chromosomes, we have discovered that the SNs are located mainly at the ends of the chromosomes of C. elegans. This suggests that, perhaps, the ends of the chromosomes fulfill some function(s) of centromeres in this species, as also indicated by the cytogenetic studies on meiotic chromosomes in spermatocytes of C. elegans, where the end-to-end association is observed. The centromeric involvement of the SNs, also found in A. thaliana, opens new horizons for the chromosome and centromere structure studies.

Keywords:

• centromere
• holocentric chromosome
• telocentric chromosome
• strong nucleosomes
• columnar chromatin

Acknowledgements

We are indebted to Prof. J. Fajkus for illuminating discussions and advice, and to Dr V. Tripathi for help in deriving the full size (R₅Y₅)₁₁ nucleosome mapping probe. We are also grateful to an anonymous reviewer for valuable suggestions.