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...

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.