Question

To promote a closer association of nucleosomes, heterochromatin protein 1 (HP1) recognizes the histone modification found in ______.

1) ceNH₃
2) H3K9me3
3) H3.3
4) H3K27me3

Answer 1

Heterochromatin protein 1 (HP1) recognizes the histone modification H3K9me3 to promote a closer association of nucleosomes, leading to the condensation of chromatin and transcriptional repression in areas such as centromeres and telomeres.

Step-by-step explanation:

To promote a closer association of nucleosomes, heterochromatin protein 1 (HP1) recognizes the histone modification found in H3K9me3.

Heterochromatin is a tightly packed form of DNA which generally contains genes that are not active or are repressed. HP1 is one of the proteins that plays a crucial role in forming this dense structure by binding to specific methylated regions on histone tails. The specific histone modification that HP1 recognizes is the trimethylation of lysine 9 on histone H3, denoted as H3K9me3. This methylation is associated with the condensation of chromatin and transcriptional repression. Heterochromatin, particularly areas around centromeres and telomeres, is marked extensively by this modification.

Answer 2

To promote a closer association of nucleosomes, heterochromatin protein 1 (HP1) recognizes the histone modification found in H3K9me3 (option 2).

Step-by-step explanation:

The heterochromatin protein 1 (HP1) is known to recognize the histone modification H3K9me3 to promote a closer association of nucleosomes. This modification is characterized by the addition of three methyl groups to the ninth lysine residue of the histone H3 protein, which facilitates the compaction of chromatin into heterochromatin, thereby reducing gene expression in those areas. The nucleosome structure that features modifications like H3K9me3 is more tightly packed than unmodified nucleosomes, and the presence of HP1 stabilizes this compact chromatin state.

Hence, the answer is option 2.