In eukaryotic cells, genomic DNA is wrapped by two copies of histone H2A, H2B, H3 and H4 and formed nucleosome. The histones can be pot-translationally modified and replaced during many metabolic processes. Histone dynamics play important roles in transcription regulation, DNA damage repair, development and many other processes. In spermatogenesis, canonical histones can also be replaced by testis specific histone variants. H2BFW is one of the testis specific histone H2B variants and is only present in primates. However, expression of H2BFW was only detectable at mRNA level, while the expression at protein level and the localization of H2BFW and the characteristics of H2BFW nucleosome are still unknown.

The histone variants influence the characteristics of nucleosomes, such as c...[ Read more ]

In eukaryotic cells, genomic DNA is wrapped by two copies of histone H2A, H2B, H3 and H4 and formed nucleosome. The histones can be pot-translationally modified and replaced during many metabolic processes. Histone dynamics play important roles in transcription regulation, DNA damage repair, development and many other processes. In spermatogenesis, canonical histones can also be replaced by testis specific histone variants. H2BFW is one of the testis specific histone H2B variants and is only present in primates. However, expression of H2BFW was only detectable at mRNA level, while the expression at protein level and the localization of H2BFW and the characteristics of H2BFW nucleosome are still unknown.

The histone variants influence the characteristics of nucleosomes, such as configuration, stability, and distribution. To learn the characteristics of H2BFW, we first identified the expression of H2BFW at protein level in both HeLa cells and mature sperm, including H2BFW153 and H2BFW175. They both can form mono-nucleosome in vivo but the cellular distributions are different. The H2BFW153 nucleosome is mainly found in euchromatin and the H2BFW175 nucleosome is mainly distributed in heterochromatin and nuclear matrix fractions. Furthermore, we also compared the difference between the canonical nucleosome and the H2BFW nucleosomes by biochemical stability assay. The results show that the stability of the H2BFW nucleosomes, especially the H2BFW175 nucleosome, are lower than canonical nucleosome. And the N terminal of H2BFW175 is the responsible for this destabilization. Since we know that RNA polymerase II has to transcribe through nucleosomes, we studied the effect of RNA polymerase II transcription in the H2BFW nucleosomes. RNA polymerase II is much easier to go through the H2BFW nucleosomes. Taken together, we identified the expression of H2BFW at protein level, and found that both H2BFW153 and H2BFW175 distribute differently from canonical H2B. Moreover, the stabilities of H2BFW nucleosomes are lower than canonical nucleosome mainly because of longer N terminal tail.

Key words: Histone Variants, H2BFW, Nucleosome Stability, Histone Distribution