Question

1. (2pt) Choose the correct statement with respect to transcription of the GAL10 gene in this yeast strain in the absence of galactose: GAL 10 WILL be transcribed because Gal4 is bound to Gal3 GAL 10 WILL be transcribed because Gal80 is bound to Gal4 GAL 10 WILL be transcribed because Gal80 is bound to Gal3 - GAL10 will NOT be transcribed because Gal80 is bound to Gal4 - GAL10 will NOT be transcribed because Gal3 is bound to Gal4 D Question 2 2 pts 2.(2pt) Choose the correct statement with respect to transcription of the GAL 10 gene in this yeast strain in the presence of galactose: GAL10 WILL be transcribed because Gal4 is bound to Gal3 GAL10 WILL be transcribed because Gal80 is bound to Gal4 GAL 10 WILL be transcribed because Gal80 is bound to Gal3 GAL 10 will NOT be transcribed because Gal80 is bound to Gal4 GAL 10 will NOT be transcribed because Gal3 is bound to Gal4

Answer 1

Haplosufficiency indicates that a single allele of the gene is sufficient to maintain normal gene function. Hence, individuals that are haplosufficient and heterozygous for a recessive allele for the condition have normal gene function as the amount of enzyme product produced is sufficient for normal gene function.

The diploid yeast cell has one copy each of wild type GAL10, GAL3 and GAL80. As this strain is haplosufficient, it has normal gene function of all three genes, despite having one mutant allele.

Gal3 is the transducer and Gal80 is a repressor and Gal4 is the transcriptional activator present in GAL regulatory switch of the galactose operon. GAL10 is the structural gene in the galactose operon. Gal4 is known to bind to N-terminal domain of UASGAL (UASG), an upstream activating region for GAL genes and activates its activation domain present in C-terminus. Binding of Gal80 to Gal4, will prevent its binding to UASGAL. However, if Gal3 binds to Gal80, Gal4 can bind to UASGAL to induce transcription of GAL10.

1. When there is no galactose, there is no galactose that can be metabolized, and hence, no GAL10 needs to be transcribed. In absence of galactose, Gal80 will bind to Gal4. This prevents the binding of Gal4 to UAS_G. Hence, UAS_G cannot activate its activation domain, thereby preventing transcription of GAL10.

Gal3 never binds Gal4. Gal3 binds Gal80 in presence of galactose only. Binding of Gal3 to Gal80 activates GAL10 transcription.

Right choice: GAL10 will not be transcribed because Gal80 is bound to Gal4.

2. When galactose is present, Gal3 binds to galactose. This binding increases its affinity for Gal80 protein. Gal3 will then bind Gal80, thereby freeing Gal4. Gal4 will then bind to UAS_G and include transcription of GAL80.

Gal3 never binds Gal4, while binding of Gal4 to Gal80 inactivates Gal4. Binding of Gal3 to Gal80 will activate GAL10 transcription.

Right choice: GAL10 will be transcribed because GAL80 is bound to Gal3.