Eukaryotic licensing factors prevent DNA replication from being initiated at origins more than once in the cell cycle. After replication has begun at an origin, a protein called Geminin inhibits licensing factors that are required for MCM2-7 to bind to an origin and initiate replication. Thus, when Geminin is present, MCM2-7 will not bind to an origin. At the end of mitosis, Geminin is degraded, allowing MCM2-7 to bind once again to DNA and relicense the origin. Marina Melixetian and her colleagues suppressed the expression of Geminin protein in human cells by treating the cells with small interfering RNAs (siRNAs) complementary to Geminin messenger RNA (M. Melixetian et al. 2004. Journal of Cell Biology 165:473–482). (Small interfering RNAs form a complex with proteins and pair with complementary sequences on mRNAs; the complex then cleaves the mRNA, so there is no translation of the mRNA; . Forty-eight hours after treatment with siRNA, the Geminin-depleted cells were enlarged and contained a single giant nucleus. Analysis of DNA content showed that many of these Geminin-depleted cells were 4 n or greater. Explain these results.
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.
Eukaryotic licensing factors prevent
initiated at origins more than once in the cell cycle. After replication has
begun at an origin, a protein called Geminin inhibits licensing factors
that are required for MCM2-7 to bind to an origin and initiate
replication. Thus, when Geminin is present, MCM2-7 will not bind to an
origin. At the end of mitosis, Geminin is degraded, allowing MCM2-7 to
bind once again to DNA and relicense the origin. Marina Melixetian and
her colleagues suppressed the expression of Geminin protein in human
cells by treating the cells with small interfering RNAs (siRNAs)
complementary to Geminin messenger RNA (M. Melixetian et al. 2004.
Journal of Cell Biology 165:473–482). (Small interfering RNAs form a
complex with proteins and pair with complementary sequences on
mRNAs; the complex then cleaves the mRNA, so there is no translation
of the mRNA; . Forty-eight hours after
treatment with siRNA, the Geminin-depleted cells were enlarged and
contained a single giant nucleus. Analysis of DNA content showed that
many of these Geminin-depleted cells were 4 n or greater. Explain these
results.
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