Nucleosome positioning along the genome is partially determined by the intrinsic DNA sequence preferences on histone. RRRRRYYYYY (R5Y5, R = Purine and Y = Pyrimidine) motif in nucleosome DNA, which was presented based on several theoretical models by Trifonov et al., might be a facilitating sequence pattern for nucleosome assembly. However, there is not a high conformity experimental evidence to support the concept that R5Y5 motif is a key element for the determination of nucleosome positioning. In this work, the ability of the canonical, H2A.Z- and H3.3-containing octamers to assemble nucleosome on DNA templates containing R5Y5 motif and TA repeats within 10.5-bp periodicity was investigated by using salt-dialysis method in vitro. The results showed that the10.5-bp periodical distributions of both R5Y5 motif and TA repeats along DNA templates can significantly promote canonical nucleosome assembly and may be key sequence factors for canonical nucleosome assembly. Compared with TA repeats within 10.5-bp periodicity, R5Y5 motif in DNA templates did not elevate H2A.Z- and H3.3-containing nucleosome formation efficiency in vitro. This result indicates that R5Y5 motif probably isn't a pivotal factor to regulate nucleosome assembly on histone variants. It is speculated that the regulatory mechanism of nucleosome assembly is different between canonical and variant histone. These conclusions can provide a deeper insight on the mechanism of nucleosome positioning. Communicated by Ramaswamy H. Sarma.
Keywords: DNA sequence motif; histone variant; nucleosome assembly; nucleosome positioning.