I. The retinoic acid receptor (RAR) is a transcription factor that is similar to steroid hormone receptors. Thesubstance (ligand) that binds to this receptor is retinoicacid. One of the genes whose transcription is activatedby retinoic acid binding to the receptor is myoD. Thediagram that follows shows a schematic view of theRAR proteins produced by genes into which one oftwo different 12-base double-stranded oligonucleotides had been inserted in the ORF. The insertion site(a–m) associated with each mutant protein is indicatedwith the appropriate letter on the polypeptide map.For constructs encoding proteins a–e, oligonucleotide 1(5′ TTAATTAATTAA 3′ read off either strand) wasinserted into the RAR gene. For constructs encoding proteins f–m, oligonucleotide 2 (5′ CCGGCCGGCCGG 3′)was inserted into the gene.NH2 f g h i j k l m COOHa b c d eThe wild-type RAR protein can both bind DNA and activate transcription weakly in the absence of retinoic acid(RA) and strongly in RA’s presence. Each mutant protein was tested for its ability to bind RA and DNA and toactivate transcription of the myoD gene in the presenceand absence of RA. Results are tabulated as follows:DNA TranscriptionalRA binding activationMutant binding −RA +RA −RA +RAa − − − − −b − − − − −c − − − − −d − + + + +e +++ + +++ + +++f +++ + +++ + +++g +++ + +++ − −h +++ + +++ − −i +++ − − − −j +++ − − − −k − + + + +l − + + + +m +++ + +++ + +++a. What is the effect of inserting oligonucleotide 1 anywhere in the ORF?b. What are the possible effects of inserting oligonucleotide 2 anywhere in the ORF?c. Indicate the three protein domains of RAR on a copyof the preceding drawing. Note that the three domainsare separate—they do not overlap.
Gene Interactions
When the expression of a single trait is influenced by two or more different non-allelic genes, it is termed as genetic interaction. According to Mendel's law of inheritance, each gene functions in its own way and does not depend on the function of another gene, i.e., a single gene controls each of seven characteristics considered, but the complex contribution of many different genes determine many traits of an organism.
Gene Expression
Gene expression is a process by which the instructions present in deoxyribonucleic acid (DNA) are converted into useful molecules such as proteins, and functional messenger ribonucleic (mRNA) molecules in the case of non-protein-coding genes.
I. The retinoic acid receptor (RAR) is a transcription factor that is similar to steroid hormone receptors. The
substance (ligand) that binds to this receptor is retinoic
acid. One of the genes whose transcription is activated
by retinoic acid binding to the receptor is myoD. The
diagram that follows shows a schematic view of the
RAR proteins produced by genes into which one of
two different 12-base double-stranded oligonucleotides had been inserted in the ORF. The insertion site
(a–m) associated with each mutant protein is indicated
with the appropriate letter on the polypeptide map.
For constructs encoding proteins a–e, oligonucleotide 1
(5′ TTAATTAATTAA 3′ read off either strand) was
inserted into the RAR gene. For constructs encoding proteins f–m, oligonucleotide 2 (5′ CCGGCCGGCCGG 3′)
was inserted into the gene.
NH2 f g h i j k l m COOH
a b c d e
The wild-type RAR protein can both bind DNA and activate transcription weakly in the absence of retinoic acid
(RA) and strongly in RA’s presence. Each mutant protein was tested for its ability to bind RA and DNA and to
activate transcription of the myoD gene in the presence
and absence of RA. Results are tabulated as follows:
DNA Transcriptional
RA binding activation
Mutant binding −RA +RA −RA +RA
a − − − − −
b − − − − −
c − − − − −
d − + + + +
e +++ + +++ + +++
f +++ + +++ + +++
g +++ + +++ − −
h +++ + +++ − −
i +++ − − − −
j +++ − − − −
k − + + + +
l − + + + +
m +++ + +++ + +++
a. What is the effect of inserting oligonucleotide 1 anywhere in the ORF?
b. What are the possible effects of inserting oligonucleotide 2 anywhere in the ORF?
c. Indicate the three protein domains of RAR on a copy
of the preceding drawing. Note that the three domains
are separate—they do not overlap.
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