Repressors are trans-acting 1'lI- heterozygote No active repressor Repressor sufficient to regulate both copies of the operator in a diploid cell. Most significantly, strain 4 showed them that the I* gene product is trans-acting, meaning that the gene product can regulate all structural lac operon genes, whether residing on the same DNA molecule or on different ones (in cis or in trans, respectively). Unlike the operator, the I gene behaves like a standard protein-coding gene. The protein prod- uct of the I gene is able to diffuse throughout a cell and act on both operators in the partial diploid (Figure 11-9). FIGURE 11-9 The recessive nature of - mutations demonstrates that the re- pressor is trans-acting. Although no active repressor is synthesized from the F gene, the wild-type (-) gene provides a func- tional repressor that binds to both opera- tors in a diploid cell and blocks lac operon expression (in the absence of an inducer). O LounchPad ANIMATED ART: " Lac repressor mutations KEY CONCEPT Operator mutations reveal that such a site is cis-acting; that is, it regulates the expression of an adjacent transcription unit on the same DNA molecule. In contrast, mutations in the gene encoding a repressor protein reveal that this protein is trans-acting; that is, it can act on any copy of the target DNA.
Repressors are trans-acting 1'lI- heterozygote No active repressor Repressor sufficient to regulate both copies of the operator in a diploid cell. Most significantly, strain 4 showed them that the I* gene product is trans-acting, meaning that the gene product can regulate all structural lac operon genes, whether residing on the same DNA molecule or on different ones (in cis or in trans, respectively). Unlike the operator, the I gene behaves like a standard protein-coding gene. The protein prod- uct of the I gene is able to diffuse throughout a cell and act on both operators in the partial diploid (Figure 11-9). FIGURE 11-9 The recessive nature of - mutations demonstrates that the re- pressor is trans-acting. Although no active repressor is synthesized from the F gene, the wild-type (-) gene provides a func- tional repressor that binds to both opera- tors in a diploid cell and blocks lac operon expression (in the absence of an inducer). O LounchPad ANIMATED ART: " Lac repressor mutations KEY CONCEPT Operator mutations reveal that such a site is cis-acting; that is, it regulates the expression of an adjacent transcription unit on the same DNA molecule. In contrast, mutations in the gene encoding a repressor protein reveal that this protein is trans-acting; that is, it can act on any copy of the target DNA.
Human Anatomy & Physiology (11th Edition)
11th Edition
ISBN:9780134580999
Author:Elaine N. Marieb, Katja N. Hoehn
Publisher:Elaine N. Marieb, Katja N. Hoehn
Chapter1: The Human Body: An Orientation
Section: Chapter Questions
Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...
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Concept explainers
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.
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Question
Looking at Figure 11-9, why were partial diploids essential for establishing the trans-acting nature of the Lac
repressor? Could one distinguish cis-acting from transacting genes in haploids?
Transcribed Image Text:Repressors are trans-acting
1'lI- heterozygote
No active
repressor
Repressor
sufficient to regulate both copies of the operator in a diploid cell. Most significantly,
strain 4 showed them that the I* gene product is trans-acting, meaning that the
gene product can regulate all structural lac operon genes, whether residing on the
same DNA molecule or on different ones (in cis or in trans, respectively). Unlike the
operator, the I gene behaves like a standard protein-coding gene. The protein prod-
uct of the I gene is able to diffuse throughout a cell and act on both operators in the
partial diploid (Figure 11-9).
FIGURE 11-9 The recessive nature of
- mutations demonstrates that the re-
pressor is trans-acting. Although no active
repressor is synthesized from the F gene,
the wild-type (-) gene provides a func-
tional repressor that binds to both opera-
tors in a diploid cell and blocks lac operon
expression (in the absence of an inducer).
O LounchPad ANIMATED ART: " Lac
repressor mutations
KEY CONCEPT Operator mutations reveal that such a site is cis-acting; that is,
it regulates the expression of an adjacent transcription unit on the same DNA
molecule. In contrast, mutations in the gene encoding a repressor protein reveal that
this protein is trans-acting; that is, it can act on any copy of the target DNA.
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