GENE EXPRESSION AND ITS CONTROL
A 377 amino acid protein (called Grn1p) was isolated from the bacterium Escherichia coli.
It contains the following amino acid sequence between residues 134-142 (Ala->His):
134 142
N….. Ala-Pro-His-Trp-Cys-Ile-Asp-Val-His…….C
Q1) What is the length (in base pairs) of the gene? Explain how you arrived at this
answer. Assume fMet is cleaved.
An E. coli mutant (designated grn1A) was isolated in the gene encoding this protein
(i.e. GRN1) and was found to make a shortened version of the Grn1 protein that
terminated within the 134-142 region (see above). Assuming that the grn1A mutant
arose via a single base pair substitution, answer the following: [NB: you will need
to consult the genetic code table (see below) to obtain your answers]
Q2) In the grn1A mutant, the His at position 136 was found to be the C-terminal amino acid of the protein. What single base change in this region (aa 134-142) would cause the synthesis of such a truncated form of the Grn1 protein?
3. Can you predict two other single base changes in this region (aa 134-142) that would also generate a truncated form of Grn1?
A second mutant (designated grn1B) was also found to make a truncated Grn1 protein with the C-terminal sequence below. The mutation was the result of a frameshift mutation and had the C-terminal sequence as follows:
134
N….Ala-Pro-His-Trp-Val….C
Q4) Is the frameshift mutation a +1 or a -1 frameshift mutation? What base was
added/deleted and at which position?
Q5) Describe which methods you could employ to confirm your predictions in (Q1-4)
Q6) Compare and contrast the organisation of the nuclear and mitochondrial genomes. (Max 800 word essay)
