Heterochromatin formation at telomeres and silent mating-type loci in yeast relies on an overlapping set of genes known as silent information regulators (SIR genes).

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#Unit 13. Methods in Biology

When the positive terminal is on the left arm, the lead is known as the aVL lead.

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#Unit 4. Cell Communication and Cell Signaling

Active JAK kinase phosphorylates several tyrosine residues in the receptor’s cytosolic domain and activates a STAT transcription factor that moves directly to the nucleus

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#Id: 3975

#Unit 7. System Physiology – Animal

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#Unit 2. Cellular Organization

The dyneins are a family of minus end–directed microtubule motors.

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#Unit 3. Fundamental Processes

isoleucyl-tRNA synthetase has a nearby editing pocket (a deep cleft in the enzyme) that allows it to proofread the product of the adenylylation reaction. AMP-valine (as well as adenylylates of other small amino acids, such as alanine) can fit into this editing pocket, where it is hydrolyzed and released as free valine and AMP. In contrast, AMP-isoleucine is too large to enter the editing pocket and is therefore not subject to hydrolysis. As a consequence, isoleucyl-tRNA synthetase discriminates against valine twice: in the initial binding and adenylylation of the amino acid (discriminating by a factor of 100), and then in the editing of the adenylylated amino acid (again discriminating by a factor of 100), for an

overall selectivity of 10,000-fold (i.e., an error rate of 0.01%).