Final answer:
The Sir proteins promote formation of heterochromatin by removal of nucleosomes from the DNA.
Step-by-step explanation:
The Sir proteins promote formation of heterochromatin by removal of nucleosomes from the DNA. Histones are basic proteins that bind to the DNA and form nucleosomes, which are the building blocks of chromatin.
The Sir proteins are involved in the regulation of gene expression by promoting the condensation of chromatin into heterochromatin, which typically results in gene silencing.