A researcher has labeled the 5? end of a DNA primer with ³²P radioisotopes. The primer can hybridize to a complementary sequence near the 3? end of a long, spliced mRNA molecule composed of three exons. The mRNA molecule can interact with two RNA-binding proteins: one of them (protein 1) binds to the first exon and the other (protein 2) binds to the second exon. The researcher uses reverse transcriptase to extend the primer in the presence of the mRNA and either of these proteins, then separates the cDNA products by gel electrophoresis, and finally visualizes the labeled DNA bands by autoradiography. The results are presented schematically in the following drawing. Assuming that the reverse transcriptase falls off the template when confronted by bound proteins, which lane (A or B) in the gel corresponds to the reaction in the presence of protein 1? Write down A or B as your answer. 
Definitions:
Skills
The abilities and expertise acquired through training or experience that enable an individual to perform tasks effectively.
Natural Rate
The level of unemployment or interest that exists when an economy is balanced, not affected by short-term fluctuations or cyclical, structural factors.
Price Level
The combined average cost of all goods and services manufactured within the economy.
Deflation
A decrease in the general price level of goods and services, often indicating an economy in contraction.
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