Tazswana’s Story by S. Catherine Silver Key

Handout 6—Tazswana’s RNA Test

Figure 6-1. RNA Hybidization Analysis of Tazswana’s RNA. The grey triangle indicates relative size of nucleic acids: larger RNA molecules migrating higher in the gel than smaller RNA molecules. Lane 1, Mr. William’s RNA sample (father). Lane 2, Mrs. William’s RNA sample. Lane 3, Tazswana’s RNA (note the two bands, one is correct size, but is also defective). Lane 4, Tazswana’s Grandmother (see Handout 2: Beta-Globin Inheritance). Lane 5, control patient with two wild-type alleles (lacking any thalassemia phenotypes). [Credit: This figure has been modified from Figure 4 in Antonarakis, S.E., et al., β-Thalassemia in American Blacks: Novel mutations in the “TATA” box and an acceptor splice site. Proc Natl Acad Sci USA, 1984. 81(4): p. 1154–8.]

Questions

1. Tazswana’s mRNA sample (extracted from her reticulocytes) has been run in Lane 3.
   
   1. Compare Lane 3 to Lane 5. In terms of pre-mRNA processing, explain why Tazswana has an extra band. Include drawings of both the mRNAs shown in Lane 3 versus the one band shown in Lane 5 (symbolize the two exons as rectangles, and the one intron as a single line).
   2. Predict how the size(s) of her mRNA bands will affect the size and amino acid content of her β-globin protein.
   3. Tazswana has one normal sized β-globin mRNA. Explain why she has severe symptoms and from whom she has inherited the intron mutation (you may wish to refer to Handouts 2 and 4).
   4. Based on these results, discuss Tazswana’s treatment options.
2. (Optional) Assume the β-globin mRNA in Lane 4 is from Tazswana’s grandmother. How is it different from the normal mRNA shown in Lane 5? Discuss the cause of this difference in terms of the mutation and why Tazswana’s grandmother is symptom free.

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