Question

Table 1: Partial RPE65 protein sequence (amino acids 41-60) for the 9-year-old LCA patient. Unmutated Protein Sequence Patient's Allele 1 Protein Sequence Patient's Allele 2 Protein Sequence START...Ser-Leu-Leu-Arg-Cyc-Gly-Pro-Gly-Leu-Phe-Glu-Val-Gly-Ser-Glu-Pro-Phe-Tyr- His-Gly...STOP START...Ser-Leu-Leu-Gin-Cyc-Gly-Pro-Gly-Leu-Phe-Glu-Val-Gly-Ser-Glu-Pro-Phe-Tyr- His-Gly...STOP START...Ser-Leu-Leu-Gin-Cyc-Gly-Pro-Gly-Leu-Phe-Glu-Val-Gly-Ser-Glu-Pro-Phe-Tyr- His-Gly...STOP Table 2. Partial RPE65 protein sequence (amino acids 61-70 and 291–300) for the 11-year-old LCA patient. Unmutated Protein Sequence Patient's Allele 1 Protein Sequence Patient's Allele 2 Protein Sequence START...Phe-Asp-Gly-Gln-Ala-Leu-Leu-His-Lys-Phe...lle-Ala-Asp-Lys-Lys-Arg-Lys-Lys- Tyr-Leu...STOP START...Phe-Asp-Gly-Gln-Ala-Leu-Leu-Tyr-Lys-Phe...lle-Ala-Asp-Lys-Lys-Arg-Lys-Lys- Tyr-Leu...STOP START...Phe-Asp-Gly-Gln-Ala-Leu-Leu-His-Lys-Phe...lle-Ala-Asp-Lys-STOP Source: Data from Russell et al. (2017). Use Tables 1 and 2 to answer the questions below. RNA codon table 12. Circle the mutations in each RPE65 allele for both patients. 13. For the 11-year old patient, assume the first Tyr in the Patient's Allele 1 protein sequence is encoded by the DNA codon 5'-TAC-3'. Using the codon table, what was the mostly likely mutation that caused this disease allele (ie what is the change in the DNA sequence)? 2nd position CIA Ser Tyr Ser | 1 pucouco pocouco Thr Thr Thr 14. For the 11-year old patient, assume the Lys amino acids are encoded by the DNA codon 5'-AAA-3'. Using the codon table, what was the mostly likely mutation that caused the disease allele in Patient's Allele 2 protein sequence (ie what is the change in the DNA sequence)? Ala Ala Asp Aso Ala Ala Glu Amino Acids NA

Answer 1

13. The mutated tyrosine is coded as 5'-TAC-3'. So in mRNA the codon is 5'-UAC-3'. The original non mutated amino acid was Histidine (which got mutated to the tyrosine). Histidine codons are 5'-CAU-3' and 5'-CAC-3'. So most likely the mutation was from CAC to UAC, i.e. a C is changed to U. In DNA it's a T to C change (transition mutation).

14. Original lysine codon 5'-AAA-3'. It is mutated to a stop codon, one of which is 5'-UAA-3'. The possible mutation thus is A to U, i.e. in DNA it is a A to T mutation (transversion mutation).