When expression of _______ is turned off in small pre-B cells,the result is the presence of P nucleotides but an absence of N nucleotides in around 50% of light-chain genes.

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The enzyme TdT is responsible for adding N nucleotides to the junctions of V, D, and J segments during V(D)J recombination in B and T cells. However, its expression is turned off in small pre-B cells, resulting in the presence of only P nucleotides and the absence of N nucleotides in around 50% of light-chain genes. Kit and CD19 are both cell surface proteins found on B cells, but they are not directly involved in V(D)J recombination. Pax-5 is a transcription factor that plays a role in B-cell development but does not directly affect N nucleotide addition. RAG-1 and RAG-2 are the enzymes responsible for catalyzing V(D)J recombination, but their expression is not specifically turned off in pre-B cells.

When Expression of _______ Is Turned Off in Small Pre-B