What is the primary composition of spliceosomes?

The primary composition of spliceosomes is indeed small nuclear RNA (snRNA) and proteins. Spliceosomes are complex molecular machines responsible for the process of splicing, where introns are removed from pre-mRNA and exons are joined together to form mature mRNA. The small nuclear RNA components play critical roles in recognizing splice sites and catalyzing the splicing reactions. These snRNAs combine with various proteins to form ribonucleoprotein (RNP) complexes, which are essential for the function of spliceosomes.

The other types of RNA mentioned, such as ribosomal RNA, transfer RNA, and microtubule proteins, serve different functions within the cell. Ribosomal RNA is a major component of ribosomes and is vital for protein synthesis. Transfer RNA is involved in bringing amino acids to the ribosome during translation. Microtubule proteins, on the other hand, are structural components of the cytoskeleton and play roles in cell shape, transport, and division. Thus, the choice that emphasizes small nuclear RNA proteins specifically addresses the splicing process and the formation of spliceosomes.