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Eating even a single death cap mushroom (Amanita phalloides) can be fatal due to a compound called α-amanitin, a toxin that inhibits transcription.
Toxins like α-amanitin are used for research in much the same way as null mutants (Chapter 16)—to disrupt a process and see what happens when it no longer works. Researchers examined the ability of α-amanitin to inhibit different RNA polymerases. They purified RNA polymerases I, II, and III from rat liver, incubated the enzymes with different concentrations of α-amanitin, and then tested their activity. The results of this experiment are shown here. These findings suggest that cells treated with α-amanitin will have a reduced level of:
a. tRNAs
b. rRNAs
c. snRNAs
d. mRNAs

Verified step by step guidance

1. Step 1: Begin by understanding the role of RNA polymerases I, II, and III in the cell. RNA polymerase I is responsible for synthesizing rRNA (ribosomal RNA), RNA polymerase II synthesizes mRNA (messenger RNA) and snRNA (small nuclear RNA), and RNA polymerase III synthesizes tRNA (transfer RNA) and some small RNAs.
2. Step 2: Analyze the experimental setup described in the problem. Researchers tested the activity of RNA polymerases I, II, and III after incubation with different concentrations of αα-amanitin, a toxin known to inhibit RNA polymerase activity.
3. Step 3: Examine the results of the experiment. Determine which RNA polymerase's activity was most inhibited by αα-amanitin. Typically, αα-amanitin strongly inhibits RNA polymerase II, while RNA polymerases I and III are less affected.
4. Step 4: Connect the inhibition of RNA polymerase II to the type of RNA it synthesizes. Since RNA polymerase II is responsible for producing mRNA and snRNA, its inhibition would lead to reduced levels of these RNA types in the cell.
5. Step 5: Based on the findings, conclude that cells treated with αα-amanitin will have a reduced level of mRNAs (messenger RNAs), as RNA polymerase II is the primary target of the toxin.

Key Concepts

RNA Polymerases

RNA polymerases are enzymes responsible for synthesizing RNA from a DNA template. In eukaryotic cells, there are three main types: RNA polymerase I synthesizes rRNA (ribosomal RNA), RNA polymerase II synthesizes mRNA (messenger RNA) and some snRNA (small nuclear RNA), and RNA polymerase III synthesizes tRNA (transfer RNA) and other small RNAs. Understanding the specific functions of these polymerases is crucial for interpreting the effects of inhibitors like αα-amanitin.

αα-amanitin

αα-amanitin is a cyclic peptide toxin derived from the Amanita phalloides mushroom, known for its ability to selectively inhibit RNA polymerase II. This inhibition disrupts the transcription of mRNA, which is essential for protein synthesis. By understanding how αα-amanitin affects different RNA polymerases, researchers can deduce the consequences of its application on cellular processes and RNA production.

Transcription and RNA Types

Transcription is the process by which RNA is synthesized from a DNA template, leading to the production of various RNA types, including mRNA, rRNA, tRNA, and snRNA. Each type of RNA plays a distinct role in the cell: mRNA carries genetic information for protein synthesis, rRNA forms the core of ribosomes, tRNA transports amino acids during translation, and snRNA is involved in RNA splicing. The inhibition of transcription by αα-amanitin will primarily affect the levels of these RNA types, particularly mRNA.