Final answer:
Accessory proteins required for assembling nucleosomes include histone proteins forming an octamer and the FACT complex for transcription. Topoisomerases help maintain DNA integrity during replication.
Step-by-step explanation:
The assembly of nucleosomes requires various accessory proteins. Primarily, the histone proteins play a critical role as they form an octamer around which DNA wraps to create a nucleosome. These histone proteins are essential as they are rich in positively charged amino acids like lysine and arginine, which enable them to bind to the negatively charged phosphate backbone of the DNA. For the dynamic process of transcription, a special protein complex known as FACT (facilitates chromatin transcription) is crucial. FACT assists in displacing histones to allow polymerase access to the DNA and then reassembles the nucleosomes post-transcription. Other proteins such as topoisomerases also contribute to the nucleosome structure by maintaining DNA integrity during replication and transcription.