Japanese researchers examined mutant alleles of a genethat encodes an enzyme, liver-type arginase, in four patients. Thenormal protein catalyzes the breakdown of the amino acid arginine.In argininemia, lack of the enzyme causes progressive developmentaldisabilities, spastic limb movements, seizures and stuntedgrowth.

The mRNA transcript for this gene codes for 322 aminoacids, but the entire gene is 11.5 kilobases long, and is locatedon chromosome 6q. Argininemia affects both sexes and is inheritedfrom carrier parents.

Patient A – homozygous for a G mutated to an A at DNAbase 365 in the gene

Patient B – homozygous for a G to C mutation at base703, which substitutes one amino acid for another.

Patient C – has patient A’s mutation and patient’s Bmutation.  

Patient D – has patient’s A mutation in one allele, andthe other allele is a deletion of a C at position 842.

The researchers evaluated the phenotype associated witheach allele by producing the encoded proteins in E. coli cells.Patient A’s abnormal protein is too short. The other mutationsyield proteins of normal length that are unstable or otherwisenonfunctional.

1. The mode of inheritance of argininemia is___________________________________________

1. Patients _____ and ______ are heterozygous for theargininemia gene.

1. Patients ____ and _____have missense mutations for theargininemia gene.

1. Why is patient A’s liver-type arginase tooshort?

2. Human liver-type arginase can be produces in E. colibecause: A) E. coli have livers B) The genetic code isuniversal C) The genetic code is triplet D) E. coli also usesarginine

3. The argininemia gene has enough bases beyond those inexons to encode ____________more amino acids.