Final answer:
The protein that forms a dimer in the linker region between nucleosomes with H3K9me3 is heterochromatin protein 1 (HP1). HP1 is crucial for the formation of heterochromatin, and it plays a significant role in regulating gene expression and chromatin structure. The correct option is (1)
Step-by-step explanation:
The protein that forms a dimer in the linker region between nucleosomes carrying the modified histone H3K9me3 is heterochromatin protein 1 (HP1). This protein is highly involved in the formation and maintenance of heterochromatin, the tightly packaged region of chromosomes. Histones and DNA interact to form nucleosomes, which represent the first level of DNA compaction in the chromatin structure. HP1 specifically recognizes the trimethylated form of histone H3 at lysine 9 (H3K9me3), a marker associated with heterochromatin.
Chromosomes exhibit even higher levels of compaction during cell division, where various proteins and histones pack the chromatin into highly condensed chromatids. Heterochromatin generally contains genes that are not actively expressed, while euchromatin is less compacted and typically contains actively transcribed genes. The involvement of heterochromatin protein 1 in chromatin remodeling exemplifies the dynamic regulation of DNA accessibility and gene expression within the cell nucleus.