Researchers have recently sequenced a number of alleles of a gene called Tas1 wh

Question

Researchers have recently sequenced a number of alleles of a gene called Tas1 which affects plant growth in the model plant Arabidopsis. The alleles only differ by a single nucleotide substitution. Plants with the allele Tas1a appear normal while those with Tas1c have stunted growth. Furthermore, the expression of the Tas1 gene is upregulated during cold stress (that is, more Tas1 mRNA transcripts are made during cold stress). You have been given some of the 5 end of the coding sequence (non-template strand) for the two alleles below. Use the codon table (right) to help you answer the questions about these sequences (Assume that the reading frame starts at nucleotide #1.) 3 9 Second letter Tas1a UAA Stop UGA SopA UAG Stop UGG TrpG 5' AAT GAG TCA TTC ATA CGT 3' Tas1c Lys AGG AUG et ACG 5' AAT GAG TCA TTC ATA AGT 3' a) Using the sequences for Tas1a and Tas1c and the codon table, show the messenger RNA sequences AND the peptide sequences encoded by this portion of the open reading frame [6 marks] for each allele

Explanation / Answer

a)

Tas1a mRNA - 5' AAU GAG UCA UUC AUA CGU 3'

protein seq - Asn - Glu - Ser - Phe - Ile - Arg

Tas1c mRNA - 5' AAU GAG UCA UUC AUA AGU 3'

protein seq -   Asn - Glu - Ser - Phe - Ile - Ser

The sequence of mRNA is always similar to the non-template strand, except that mRNA contains Uracil instead of Thymine. So, the sequence of Tas1a and Tas2a mRNA will be similar to non-template strand and T is replaced by U in mRNA.

b) The single nucleotide substitution in the Tas1c mRNA resulted in the coding sequence of Tas1c mRNA. This resulted in the translation of protein with Serine amino acid in the place of Arginine.

This substitution of serine amino acid would have affected the activity of Tas1 protein making it inactive and thus stunted growth.

c) Cold stress activates stress response proteins and downstream kinases which results in the activation of the transcription factors in the nucleus. These transcription factors bind to the promoter region of Tas1 gene and promote the transcription of Tas1 mRNA by recruiting proteins required for transcription.

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