Final answer:
SIR2 is the protein involved in heterochromatin formation through its role as a histone deacetylase that removes acetyl groups from histone tails, leading to condensed chromatin and reduced gene expression.
Step-by-step explanation:
In the context of heterochromatin formation and histone modifications, the protein SIR2 is involved in the deacetylation of histone tails. This enzyme functions as a histone deacetylase and is associated with gene silencing in yeast. Its role involves removing acetyl groups from lysine residues on histone tails, leading to a more condensed chromatin structure known as heterochromatin. This chromatin conformation is less accessible to the transcription machinery, which results in decreased gene expression.
Heterochromatin formation is significant in terms of regulating gene transcription and maintaining genomic stability. Enzymes such as histone deacetylases, like SIR2, and others like histone methyltransferases contribute to the highly dynamic nature of chromatin remodeling through modifications like histone acetylation, methylation, and deacetylation.
Note that although other proteins are listed in the question, such as SIR3, SIR4, RAP1, and Cdc13, it is SIR2 that is specifically known for its histone deacetylase activity and involvement in heterochromatin formation.