Chapter 13, Problem 31ESP

M. Klemke et al. (2001) discovered an interesting coding phenomenon in which an exon within a neurologic hormone receptor gene in mammals appears to produce two different protein entities (X Lαs and ALEX). Following is the DNA sequence of the exon’s 5′ end derived from a rat.

5′ -gtcccaaccatgcccaccgatcttccgcctgcttctgaagATGCGGGCCCAG

The lowercase letters represent the initial coding portion for the XLαs protein, and the uppercase letters indicate the portion where the ALEX entity is initiated. (For simplicity, and to correspond with the RNA coding dictionary, it is customary to represent the coding (non-template) strand of the DNA segment.)

1. (a) Convert the coding DNA sequence to the coding RNA sequence.
2. (b) Locate the initiator codon within the XLαs segment.
3. (c) Locate the initiator codon within the ALEX segment. Are the two initiator codons in frame?
4. (d) Provide the amino acid sequence for each coding sequence. In the region of overlap, are the two amino acid sequences the same?
5. (e) Are there any evolutionary advantages to having the same DNA sequence code for two protein products? Are there any disadvantages?