43 CFR §30.261

1. (a)To exercise its option to purchase, the tribe must file with the agency:
   1. (1)A written notice of purchase; and
   2. (2)A certification that the tribe has mailed copies of the notice on the same date to the judge and to the affected heirs or devisees.
2. (b)A tribe may purchase all or part of the available interests specified in the probate decision. A tribe may not, however, claim an interest less than decedent's total interest in any one individual tract.