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-In-Ala-Leu-Leu-Tyr-Lys-Phe...Ile-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 | 2nd position 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)? CAG Poco Poco Poco Poco 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)?

Answer 1

Question 12

Answer: Mutation in each RPE65 allele for both patients are circled in red color. For the 11 year old pateint, allele 2 protein sequence is terminated prematurely due a mutation that resulted in stop codon.

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-LeufTyr 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

Question 13

Answer: For the 11 yeard old pateint, first His in unmutated protein sequence is mutated to Tyr in the patient's allele 1 protein sequence. It is given in the question that Tyr is coded by 5'-TAC-3' codon. The likely mutation that caused this disease allele is substitution mutation (C is substituted by T ). His in unmutated protein sequence is coded by 5'-CAC-3' codon. Mutation of C to T in this codon results in 5'-TAC-3' codon that codes for Tyr.

Question 14

Answer: For the 11 yeard old pateint, third Lys is encoded by the 5'-AAA-3' codon. Mutation in this codon results in a stop codon (5'-UAA-3') in the patient's allele 2 protein sequence. Hence, likely mutation that caused this disease allele is substitution mutation (First A is substituted by U ). Lys in unmutated protein sequence is coded by 5'-AAA-3' codon. Mutation of first A to U in this codon results in 5'-UAA-3' codon that codes for stop codon.