ABSTRACT
The development of methods for isolation of nucleoli provided the basis for many investigations on nucleolar structures, their components, and their functions. Although, initially, studies were made on nucleolar histones, with improving technology the opportunity existed to define the numbers and types of nucleolar proteins and to evaluate their changes in the course of altered nucleolar functions. There are many more nucleolar proteins than were originally suspected. The earliest estimates of the numbers of nucleolar proteins noted that nucleoli contained histones, synthetic enzymes such as the ribonucleic acid polymerases, and proteins that were in pre-ribosomal or ribosomal particles. One of the important procedures in analyses of nucleolar proteins is the separation of particulate elements from soluble and other nucleolar elements. A most important observation in studies, which has not been clarified, relates to the existence of small particles at the ends of the branches.
