If the business or rental part is within your home, such as a room you use for a home office, you will not need to allocate your basis and the amount realized on the sale. And you will not need to file Form 4797 for the portion of the sale corresponding to the business or rental part. But you will need to include any depreciation you have claimed or could have claimed as a deduction on the business or rental part after May 6, 1997 in your taxable income.
For example:
You owned your home and lived in it as your main home for the last four years.
You have a room in your home that qualified as a home office for tax purposes.
You claimed total depreciation deductions of $2,000 for business use of your home, for your home office.
You sold your home for a gain of $120,000.
You meet the ownership and use tests, so you can exclude the gain on the sale. Since your home office was inside your home, and not separate from it, you do not need to allocate the basis and the amount realized on the sale between the personal and business portions of your property. But you cannot exclude the part of the gain equivalent to the $2,000 of depreciation deductions you have claimed. You would report the entire gain of $120,000 on Schedule D. Your exclusion would be $118,000, and you would report $2,000 as a taxable gain.