A cDNA library is made with mRNA isolated from liver tissue. When a cloned cDNA
ID: 72275 • Letter: A
Question
A cDNA library is made with mRNA isolated from liver tissue. When a cloned cDNA from that library is digested with the enzymes EcoRI (E), HindIII (H), and BamHI (B), the restriction map shown in the figure below, part (a), is obtained. When this cDNA is used to screen a cDNA library made with mRNA from brain tissue, three identical cDNAs with the restriction map shown in part (b) are obtained. When either cDNA is used to synthesize a uniformly labeled 32P-labeled probe and the probe is allowed to hybridize to a Southern blot prepared from genomic DNA digested singly with the enzymes EcoRI, HindIII, and BamHI, an autoradiograph shows the pattern of bands seen in part (c). When either cDNA is used to synthesize a uniformly labeled 32P-labeled probe and used to probe a northern blot prepared with poly(A)+ RNA isolated from liver and brain tissues, the pattern of bands in part (d) is seen. Which of the statements that follow are true? If the first is false and the others true, enter FTT.
These cDNAs are probably derived from the same gene.
The bands seen on the northern blot are of different sizes because transcription in brain and liver cells start at different promoters.
The two different restriction maps indicate that there are tissue-specific transcripts produced by alternate splicing.
a) E H 1.1 0.9 0.5 0.6 1.3 b) E 1.1 1.2 1.3 kb e) E HB 8539 d) Liver Brain Size (kb) 7.8 (kb) 3 _3.6 2.0 1.3Explanation / Answer
TFT: 1st is true, 2nd is false and 3rd is true.
These cDNAs must be derived from the same gene, thats why the probes designed with either of the two cDNAs gave same bands pattern and plots.
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