Question

You are studying P-glycoprotein in human populations, and find two gene sequence variants that appear to influence its activity. Their variant mRNA sequences are given below (codons in the correct reading frame are separated by spaces):

…GGA GGC UCC CCC CCU CGU GAG GAC CUG AAG…  

Variant 1         …GGA GGC UCG CCC CCU CGG GAG GAC CUC AAG…

Variant 2         …GGA GGC UCA CCC CCU CGA GAG GAC CUA AAG…

HeLa cells were transfected with genes for each of the three variants. The ability of each variant to pump the Rh123 fluorescent dye in the presence of digoxin was evaluated using flow cytometry.

1. Which variant should give cells expressing it the highest fluorescence intensity?

2. Which variant should give cells expressing it the lowest fluorescence intensity?

3. Explain your answer.

Answer 1

there are 3 mutations in the gene sequence which resulted in the variants;

1st muation in 3rd codon, UCC, which changed to UCG in variant 1 and to UCA in variant 2.

however, all the codons (unmutated and mutated) codes for the same amino acid, Serine.

hence, there would not be change due to this mutation.

2nd muation in 6th codon, CGU, which changed to CGG in variant 1 and to CGA in variant 2.

however, all the codons (unmutated and mutated) codes for the same amino acid, Argenine.

hence, there would not be change due to this mutation.

3rd muation in 9th codon, CUG, which changed to CUC in variant 1 and to CUA in variant 2.

however, all the codons (unmutated and mutated) codes for the same amino acid, Leu.

hence, there would not be change due to this mutation.

All the cells would exhibit similar fluorescence intensity.